The issue I see is AT&T has too many things that aren't complete at one time. Converting edge areas to 3G, converting 3G area to HSPA+, converting whole network to LTE.
I think the biggest one would be getting edge areas to 3G. From reading it looks like a lot of AT&T network is still edge, if that's true that's a shock to me.
How much of VZW is '3G' compared to AT&T network? If VZW network is almost 3G it makes sense for VZW to deploy LTE because their network is almost entirely '3G', speeds being irrelevant. If AT&T network needs more edge to 3G then I don't understand why they wouldn't convert those areas to 3G.
AT&T just seems they have too many open ends.