I think that WotC could have prevented a lot of ill will by marketing 4e as a separate game, while continuing with the 3.X architecture. Call it D&D Essentials to tie it in with the older property, and market the new game as an adjunct or alternative. The market might still have split, but WotC would have controlled both sides of the divide.
The Auld Grump
Could have been an option. But I doubt it was actually practical. When WotC changed to 4e, they have already released so many supplements and were running out of new things to release. Unless, say, they have released something like 3.75e, they could not wrote more supplements which sells well, IMHO.
Personally, I both love and hate 3.Xe. While it is a good game, playing 13+ level games are too complex. During those 10 or so of years, I have actually ran several campaigns which started at L1-4 and reached to the higher levels. One of them actually reached to L21+. They were fun, I say. But if you ask me, I don't want to do it again.
And I do love 4e. Yes, the game has new problems of it's own. And it lost something 3.5e had. But 4e is still a good game and, for me, frankly speaking, MORE D&Dish. Because, my first D&D was BECM D&D and not AD&D.
Regarding Pathfinder, well... I am ignoring it completely. It is too similar to 3.5e and seems not having much improvements. On the other hand, Pathfinder is too different from 3.5e that they cannot be mixed easily. And actually, I strongly dislike some of the changes made in Pathfinder.
When I want to play a 3.Xe style game, my 3.5e books serve me well. I don't want to buy new bunch of books again, just to play something slightly different from 3.5e but not a true improvement.