I believe that to a very large extent, being a good player is a skill not an art.
Being a player takes skill as well. The only reason I wouldn't say its absolutely a skill is that I've had players who were naturally skilled at most of what makes a player a good player.
If you read the 1st edition DMG, there is this thread that runs throughout it, that the primary job of the DM is to create an environment for the players that rewards 'skillful play'. And by 'skillful play', Gygax means the ability to overcome adversity, to manage the resources the DM provides efficiently, to be creative problem solvers, to learn how to interface with and manipulate an imaginary environment, to use good tactics, to stay focused on your goals, and so forth. Gygax believed that the game was designed or should be run such that those players which 'played well' excelled, and those players that didn't 'play well' would learn how to play well so that they too would excell.
This is an idea that I find is somewhat sadly falling by the way side. Yes, it is true that if the DM sees his primary job as 'providing obstacles', that it can lead to antagonistic play if you aren't careful. And, yes, it is true that if the DM sees his primary job as 'providing obstacles', that it can result in a situation where the players don't feel like they are being rewarded properly for their efforts - Gygax doesn't deny any of that, and in fact specifically addresses it. But, I can't help but feel that the emphasis on 'fun', oddly is leading to styles of play that I find to be a lot less fun (as a player).
It's not just in D&D or even just in PnP games. If you go back and play an 1980's video game, what you are going to find in most cases is a game with a very steep learning curve. The first couple of times that you play 'Donkey Kong' or 'Centipede' or whatever, you are going to be lucky to get more than a few seconds into the game without dying. In fact, almost all the hardest games ever devised are 1980's arcade games. To actually get pretty decent at a game like 'Ghosts and Goblins', and by that I mean 'surviving the first stage', you might need to play 100 games or more. Very very few players were ever able to say that they 'beat the game'. Beating the game was not the expected outcome. Even a game like 'Super Mario World' will defeat a novice gamer a couple of times before they get very far into it.
If you play a modern console or arcade game, you often have a very different experience. If you play a game like Diablo II, you might not have a death in the first 5 or 6 hours of play and beating the game is the expected outcome for all players. In other words, the game is only so difficult that least decicated and casual gamer can also beat the game. Everyone beats the game, and quite often on their first try. If you go to one of the web sites that have free flash games, which to me are the true successors of the old arcade games, you'll consistantly find a game which everyone doesn't beat in the first few times that they play it will be criticized by players as 'too hard'.
Conversely, I find myself rating many very popular games than the average because they are 'too easy'. I played one shooter game, and beat it on the first try without losing a single life. I commented that the game was too easy, and that there was something seriously wrong with a shooter that you could beat on the first try. I was objectively wrong, because the game has since gone on to be the most popular shooter on the site - and many of the shooter's I consider far superior in terms of design and play are rated quite badly because they are 'hard'. But to me, 'hard' is a very good thing, because if it is 'easy' I can't play the game for very long. I beat the game and its over, and then I must move on to something else.
I've long understood that the fundamental basis of all enjoyable games is that they provide the illusion of accomplishment. In other words, all games are a 'waste' and provide no direct benefit to the player, but they fun because in playing a game we can feel as if we accomplished something grand. In most people's lives, accomplishing something grand is a rare achievement, and playing life as if it was a game to win would be among other things far too stressful and demanding. Playing games gives us this feeling of satisfaction that we have accomplished something, even when we understand at one level that we haven't. Good games provide real feelings of accomplishment.
What I've noticed is that over the years, the way games in general accomplish that has been changing. We are moving toward a culture in gaming, or at least in video gaming and role-playing gaming, of 'everyone wins' and the player base for these games largely feels a game is most fun if everyone wins all the time. To some of us though, to paraphrase the by now cliched description, "If everyone wins, then no one does." The games don't encourage what Gygax called, 'skillful play'. As result, when some young gamer faces a shooter that he can't win in the first couple of tries, he gets frustrated. He's not used to being expected to develop a skill set, much less a very particular and specialized skill set. The designer of the game is now in his opinion interfering with his fun, because he has been deprived of the sense of accomplishment he expects when playing a game. But this is of course wholly incompatible with a player who derives that since of accomplishment entirely and precisely from developing those specialized skill sets (however useless they may be in the real world).
What has this to do with XP, you may ask? Well, Gygax treated XP like it was a way to keep score. Skillful players not only survived the dungeon, but dug more treasure out of the dungeon at less cost, and so obtained greater XP. Advancing a character to new heights of experience (before that character died), was how a player knew that he was playing more and more skillfully. Eventually, after much struggle, some players might be rewarded with very powerful characters indeed, but only after mastering Gygax's idea of 'skillful play'. (Those players with too much hubris, could be treated to something like 'Tomb of Horrors' to bring them back down to earth.)
There is I think a trend to get away from this and to consider it quite 'old fashioned' and primitive, inferior, unsophisticated, and obselete. There is this trend to simply level up the party when the DM thinks its time, or to award everyone an arbitrary amount of XP. Maybe it works. I don't know. But I think that if you did this, you'd be very much in danger of leaving behind the notions the game was founded on, like 'skillful play'.
I suspect that when I post this, alot of irate players are going to jump on me and say that the games that they play are still hard, and that TPK's are still possible or even perhaps common. I think that largely misses the point. I think its quite possible to create a game that is hard, without the game meeting the requirements I outlined. In particular, I think back to when the game 'Gauntlet' was introduced to the arcade. It smash success. Everyone lined up to play, and it was alot of fun because it was one of the first multiperson cooperative experiences (not the absolute first, but one of the first, and certainly the first big success). But it was hard to escape the realization that it was something new in terms of game design, because your life drained continually and as a result, even very skillful play wasn't that much more successful than low skill play. The real secret to progressing was usually just pumping in more quarters. It made alot of money, but it created the notion of a 'quarter eater' - a game that provided a certain number of minutes of play per quarter, but which capped out the skill you could obtain in some fashion so as to ensure that no one would ever be so good as to play for hours on end on a single quarter they way they might eventually on the older style games (including the ones that killed you within seconds the first time you played).
Anyway, my point is that I largely agree. Calculated XP is still important, at least to me, in gaming. If I played a game where the XP was arbitrarily assigned, I'd somehow feel cheated.