This thread is about a response to the „old school revival“. And the OP seems to think that a lot of that has to do with a feeling of nostalgia and almost nothing to do with how the systems actually compare and are played. I do not think I agree too much.
I do think that we can discuss different editions of a role playing system without starting an edition war. I think that you can compare different editions and what their mechanics mean for the style of play without being insulting. After all, everybody is entitled to their own opinion and there is no objective way to measure a good or bad way to play a roleplaying game, since it is a only a game and not some sort of life saving medical procedure.
But I do think that rule systems have a strong influence on the style of play. When you play Harnmaster, for example, you look at combat in a different way, because it is far more deadly than a DnD combat. When you play Warhammer FRP, there is a different way to play as well, because all the character classes are conceptually so much an integral part of the world already. And if you play with a system that offers no rules for the use of skills, for example, that is a different game, too, I think.
I started to play roleplaying games in the early 80s, back when an elf was a mixture between a magic user and a fighter, a fighter was a human and a dwarf was, well, a dwarf. I am not a follower of the „old school movement“ and I think this thread is about giving noninsulting reasons for that.
Looking back at the basic DnD system, one first thing comes to mind: The lack of rules for many things that seem so commonplace in today's systems: skills, specific combat maneuvers, etc. In general, the DM had to come up with rules for this on her own. In the group I played back then, we, for example, decided to use the skill system of the german game „The Dark Eye“ at some point, because there was nothing else there. Maybe there was, but we just did not know about it then.
Today, I prefer to play with a system with rules that cover all the important aspects of in-game situations. And skills are important. This is because I as a DM feel that I should have to spend less time improvising rules and rather spend my time thinking about the story we would like to play. Please, I am not saying that this in not something old schoolers do (thinking about a great story that is), do not get me wrong. But I am of the opinion that having to come up with rules on your own uses more time in addition to coming up with a story.
Secondly, the way a DM rules certain things is heavily dependent on the quality of the DM. With a system like 3.x or 4e, you can assume the rules have been playtested and work. I know that there are exceptions, but these are even more apparent with homebrew rules, I think.
And what if I forget to write the rule down and the situation comes up again? Will I remember the rule from three weeks ago? Or will the other players have to remind me?
To sum it up: It is easier to play with a system that offers coherent rules that everybody can look up and that do not rely so much on the whim of a single person. To me, this is more fair, too, because there is more mechanical control in the hand of the other players and not just in the hands of the DM.
The second thing that plays a part is the lack of balance that „old school“ modules offer in my view. Looking through the B-series and the X-series of adventure modules, I cannot remember the encounters being balanced in a way. It even says sometimes that an encounter could be too much for the PCs and then they need to run or find some other way to survive.
Again, there are those who like it that way, and if they want to play like that, that is fine with me.
The reason why I am glad that „modern“ adventures follow a different concept is that I feel that running away is useless if there is no story reason for it. Useless from a story and experience point of view. Running away can be dramatic and fun and make a good story. But to have to run away just because the DM rolls up the wrong monster on a „Wandering Monster Table“ is not for me.
So, yes, there are major differences in the style of play. And I think that is why „old schoolers“ like the older versions so much. Because they like to play that way. And I do not. Not anymore. I do not feel insulted by their view. And I hope I have not insulted anybody with my point of view. Or with the fact that this is a very long post.