There's a difference between mother in the hospital, double-book with a pub crawl, and just forgot as excuses.
There is - but it's not a distinction that I personally care to make. YMMV. The way I look at it, if I like someone well enough to keep inviting them into my home, into my campaigns, them I'm willing to cut them some slack.
Besides, sometimes a soul needs a good pub crawl

. As a matter of fact, I'm somewhat overdue...
2) Levelling everyone as a group removes the ability to reward creative thinking, role-playing, good behaviour, and the like with experience. Should alternative rewards be in the game? Either as part of the core rules or as a module.
I don't think this is true (at all).
The reward for creative thinking and good role-playing is
success; the PCs achieving their desired outcomes with the minimum undesired consequences.
I get the need for a positive feedback loop during play, but rewarding players with metagame currency after the fact isn't the only way to get it.
The best reward for a cunning plan is having it
work.
Really? I think you're rather underselling the basic notion of a game (in which achievements defined by the rules are attributed meaning by participants and observers). For example, I think many people feel rather strongly that the San Francisco Giants recently achieved something greater than "fun" simply by playing a game (while the same "fun" is not much of a consolation prize for the other teams). The sense of achievement from performing well in a game, arbitrarily defined as its rules might be, can be a major driving force in people's lives.
True -- but RPGs aren't competitive games the way baseball games and chess matches are. Victory is terribly subjective; the PCs 'win' against 'teams' assembled, coached, and deployed by a referee who's job is to challenge them, or simulate events in a fictional world, not take home the trophy. The rules are flexible guidelines, prone to being modified on the fly or even switched on and off on a case by case basis (they're more erratic, even, than penalty calls in American football!).
Achievements are pretty subjective, too. Sure, there's PC survival and weath/power gains, but there are also intangibles; story rewards, character growth (in terms of characterization, not level), rewarding relationships in the game's fiction. Not to mention 'achieving' really entertaining failures.
For example, some of the crowning achievements of out old 4e campaign where
character tag lines, like Lizzy the Communist Dwarfs battle-cry "Universal Health Care!".
Where was I? Oh... the joy of RPGs is that people get so many different things out of them, there are many different kinds of success. I suppose I could hand out bonus XP to players for 'hitting their marks' (however they define them), but I choose not to. Mainly because I refuse to reward players for playing the way I do -- and I'm fully aware that's
exactly what I'd end up doing if used individual XP awards.
(I'm well acquainted with my own inescapable subjectivity)
So I let the reward for good play be in-game success and fond memories, and leave XP as a pacing mechanism.
There's also the creative aspect of the game, which can constitute artistic achievement. Not that many people will ever see it, but there are many great artists toiling away in obscurity, some under the auspices of playing an rpg.
Absolutely -- but I one thing I refuse to be as DM is an art critic. Again, artistic achievements in my campaigns -- such as they are -- are rewarded through the player's talking about other peoples' PCs/exploits years later.
Certainly, I can see the motivation to want to recognize player achievement by "keeping score" using XP, even though I don't do it.
I think campaigns that push the game aspect of the game really benefit from XP as an explicit score-keeping mechanism -- they're just not the ones I run (but I'd be game to play in one).