To be fair to DocM, It is definitely different from the Core D&D rules - if it weren't we wouldn't be interested in it.
So, in one sense, it IS d20 (in that it's not a vastly divergent system) but it ISN'T d20 (in that many of its precepts would require you to use certain mechanics differently, such as spells, class abilities, truenaming, etc.)
I'm happy with both, but darn it, I'm torn as to whether to buy 3E revised. One one hand, I would be just as content to download the SRD and note changes, but I'm planning on going to GenCon, and going to GenCon without buying the 3E revised books would be like going to a pub to drink lemonade.

I may wind up going for a thumb-through of BOTH at Gencon, and seeing which one I want more, and buying that one on the last day.
Then again, Monte might experience a huge run on the books if they are wildly popular, and my fence-straddling may get me in trouble, and I'll have to order it online, because certainly none of my local stores will carry it.