I'm really not seeing what you're seeing Reynard, but, I do think it's an interesting observation to claim that earlier editions advocated a fundamental switch in gameplay by back-loading the XP charts so that advancement slowed down. If anything my own experience of AD&D 'supports' this, in that we did have PC's with keeps and so-on, but I would be looking through rose-tinted glasses if I thought that the games we played ever got to the point where XP, treasure, magic items, the dispatching of enemies, and general hit-point-related violence took second place to political wrangling, the governance of territories, the maintenance of keeps, or anything like that.
Sure, our name characters had keeps. We had little tables which told us how much gold we'd have to take out of our coffers "every month" in order to support and maintain a fleet of butlers, guardsmen, cooks, bards, etc. But it was a quaint diversion at best, a bragging right. Somewhere to retire to between adventures, somewhere to draw little maps of if we felt in the mood. The mechanics which supported these diversions never, ever caused the game to morph into anything other than, well, D&D. The party keep was somewhere we retired to between various bouts of adventuring, and if anything, the gradual decline in advancement caused way more campaigns to fold, and favourite adventurers to retire, than ever caused the campaign to change to accomodate the lack of options.
So, I fail to see a shift in the way I've played the game through the editions, and I can't agree that systemic changes have somehow flattened the experience to a point where 30th level is "the same" as 1st level in everything except your tactical options. The campaign changes around the players, the people they're dealing with change dramatically, the problems they have to solve change in grand orders of magnitude. This, to me, is no different than the process which occured twenty years ago.