Who cares about the 2.2 update? Only Android geeks who weren't going to buy an iPhone4 anyway. I don't see them delaying the update specifically to "boost" the iPhone... but that doesn't mean they'll be in any hurry to get it out the door either.
Of course, IF AT&T IS about to lose exclusivity on the iPhone, then they will want to boost their Android cred since Android seems to snowballing into the mainstream - or at least they would if they were smart.
That said, this is all speculation until Our Father, Steve Jobs The Magnificent, walks on stage and announces the best iPhone ever, now on Verizon.