Welcome to the Grog Side.
I understand what you're saying, I think, because I too love D&D. And I want to embrace the products put forth in association with the brand. But, D&D is something definite. Not that the definition of D&D is something very narrow, but it does have an essence... that's how we can use it intelligibly in a sentence. But a lot about D&D is changing in 4E.
Now, there are two kinds of things you can change: essential things, and non-essential things. I think that a perfect example is AC... as we all know, in pre-3E, AC was descending. 3E changed it to ascending. To me, that's a perfectly fine sort of change, a non-essential one. The game isn't all the sudden something else because they reversed the way AC goes. Now, maybe the change was prudent or maybe it was unnecessary... that's a different discussion. But there's nothing fundamentally transgressive to the nature of D&D involved in that change.
To me, some fundamental assumptions of D&D had been changed in 3E, which I see as ultimately causing it to be a game that I don't care for. Such as the notion of the "character build", which I consider to be foreign to the original concept of the D&D (but we don't have to hash that out here). The net result of adopting the "character build" philosophy, however, was that a different sort of play experience was delivered. The sum total of these play experience differences drove me away from the game, and back to previous editions and their spiritual inheritor, C&C.
But, I'd still like to have the chance to buy new products. I'd love for 4E to be true to the spirit of D&D but with changes that are good for the game itself (as opposed to being good for making it into some different game that isn't D&D, or good for marketing, etc.).
So there's something that really misses the point when somebody turns to the grognard and says "Well just play the old edition that you prefer." How does it miss the point? Because the grognard looks at the edition he loves and says "Please, do more like this!" The grognard will even embrace changes to the rules, as long as they are in the spirit of the game.
Consider football: it is possible to add or subtract certain non-essential rules, like "Instant Replay". Some like it, some don't, but nobody can seriously claim that you're not really playing football if it's in or it's out. However, what if they changed it to where you only need to make 2 yards for a 1st down? Or they decreed that the Quarterback will now ride around the field in a dune buggy? Whatever the good or bad things that could be said for those rules changes, they'd leave you with something that was decidedly not football, regardless of what the NFL would try to call it.