Thinking about my post, and the comments I received, I came to this conclusion, which I think states my point a bit more succinctly.
TSR D&D has an unstated but implied 'goal' of the game--exploration. Leveling up is a reward within the game, but not the main point of playing. Leveling up helps you with exploration, but careful play at low levels will result in successful exploration without levels.
WotC D&D has an unstated but heavily implied 'goal' of the game--leveling up. Exploration results in some rewards, but it's not the main point of playing. Gaining that next level so you can continue your 'character build' is the point.
I think that boils it down to the essence. 3E and 4E are about the metagame exercises. That's where the fun supposedly lies. That's why you don't need a sense of advancement or greater power as you level up, because what they think is fun is deciding how to customize and improve your character as you level. It's about the destination rather than the journey.
Lots of people like that. I'm not one of them.
Older editions are about the journey. How you get there is where the fun is, and the rewards are just that--rewards, not a goal unto itself.
I think this ties in with my earlier posts about XP for activities outside of combat, and character motivations, and all that. Also, with my idea that the 'special abilities' of most high level characters ARE their magic items--the rewards of exploration in game, assuming most old school campaigns don't have magic shops in every town.
Hmmm, my nice simple post to clarify things now turns into something I need to think about a bit more...