For the vast majority of iPhone users, whatever exists in the store is just fine and dandy, and while not being able to use Google Voice natively etc might be an annoyance, the probability that an average user is

a) aware that an app they might use often has been actively rejected from the store and b) feel that the functionality provided by said app is important enough to switch phones to have

seems pretty low. The fact that you read a site like HN and know the dramas surrounding rejected apps colors your thoughts on the subject heavily.

And tethering isn't there -- AFAIK -- because of AT&T, not because of Apple.