They have been in this race since the first release of Windows CE in the late 90's. They even dominated the segment for quite some time.
WP7 is supposed to be cleaner. I don't use it currently, but will be interested when I have the chance (probably later this year).
In a sense, each platform requires that you "adopt" their platform of choice. iOS - OSX, WinCE - Windows, Android - Eclipse (and you aren't going to tell me Eclipse is actually superior to OSX or WinX or Linux -- it is bloated, kludgy, and has it's own quirks -- but it is the easiest platform for android dev)...
That said, the worst mobile dev. platform I've ever used was Symbian. On Windows it was a jumble, on *nix/OSX it was a trip into insanity.
I know a lot of people are happily coding Android apps with Vim or Emacs and command line tools too.
Will Apple and Google head down this path? Unlikely, it seems to be worth more money now than ever.
Will it happen to Apple and Google? Not sure. Possibly.
When companies get big, they start to abhor change. Change is what keeps companies smart.