[schettj]

It's the same reason why you have to "jailbreak" your iPhone or ipod touch in Apple Land.

If they control the hardware *and* software, they gain several advantages
* forced obsolescence (more so in the WimMo case, since the carries refuse to provide updates)
* easier support (need only train reps on one, or at most a couple releases)
* reduced risk of failure during upgrades (people do the darnedest things)
* better control of the user experience

In the case of WinMo up until recently greed was the name of the game. Get as much as you can out of the customer... Mostly on the carrier side, but HTC I'm sure didn't mind. Apple claims the last reason is their primary one - "to protect people from themselves" mostly.

The game is changing, fortunately.