"Apple might as well not care and happily approve the app if such terms didn't exist?"
Likely so. Note that there is a Skype app for the iPhone but it is restricted such that it will only make voice calls through wifi. It's rumored that AT&T has been opposed to VoIP traffic over its 3G data network though it has just recently finished work necessary to make such things feasible and may reverse its earlier decisions (paving the way for full-featured skype and google voice iPhone apps).
But GV isn't a VoIP service. So AT&T opening up its 3G network to VoIP traffic will have no effect on Apple's decision to accept or reject a GV app, and it can't have played any part in the original rejection.
How is Google Voice not VoIP? When one uses Google Voice one's voice is transmitted over an IP network, that seems to be the very definition of VoIP. Attempting to claim otherwise would seem to be to play semantic games.
I'm sorry, but you are mistaken. Your voice is not transmitted over an IP network with Google Voice. That's why it's not VoIP. There are no semantic games involved. Since I feel like I've beat this to death a few times before, I'll just point you to this: http://www.itworld.com/print/75774.
And yes the Wikipedia entry for Google Voice is mistaken. I should probably fix that for them...
Likely so. Note that there is a Skype app for the iPhone but it is restricted such that it will only make voice calls through wifi. It's rumored that AT&T has been opposed to VoIP traffic over its 3G data network though it has just recently finished work necessary to make such things feasible and may reverse its earlier decisions (paving the way for full-featured skype and google voice iPhone apps).