Why would you expect that?
AT&T not only was late to the Android party, they sacrificed the few meager offerings they had because the iPhone was their smartphone of choice.
If you were drawn to an Android device, it was unlikely it was at AT&T because even once they started carrying them, they carried the dregs like the Backflip. Instead you were choosing from every other carrier. If you wanted an iPhone, on the other hand, you were going to AT&T (hence why AT&T paid big dollars for the exclusivity, and it showed in their subscribership numbers).
Verizon's breakdown will be nothing like AT&T's.
Further, AT&T is suddenly in the Android game in a big, big way. I hear there's something like 20 top-flight 4G Android devices hitting AT&T in the next few months, including the leader of the pack Motorola Atrix. So from being the iPhone place, AT&T is almost switching to be an Android-dominated carrier.
I think this whole "iPhone was only on a single carrier, let's see how things change now!" thing is going to turn out quite unlike how many so desperately hope.