Why should we be grateful for mouse support? If we had to just use the keyboard it would be terrible
Nobody would be expected to own a 360 controller for gaming on their PC, so developers are forced to put mouse control in no matter what.
There's a fair amount of talk of 'extras' on the PC version, and yea ok there's an effort on the part of developers to have that in there, but that's not so much a case of doing something because they want to make it 'better for some, but not for others', but rather adjusting to the control interface and the game control experience which it allows for. This difference is often reflected in visual interface.
One game that did this incredibly well was Mass Effect 2. Comparing the PC to Xbox 360 versions, there were certainly differences in things like minigames, menu, interface control etc. but most importantly the PC version actually *felt* entirely like it was developed with K+M in mind, whereas the 360 version felt like it was developed with a 360 controller in mind.
It's effort, yes, and if developers don't want to take those steps for one platform then they'll end up with an inferior product. But frankly that's their problem if the response to their game isnt as good as it could have been.