1) Has it occurred to anyone that it is exclusive with AT&T because a GSM version is ready to go, but they are still working on something that will fly with Verizon? It would not be the first time that has been the case.
2) Of course, not to burst anyone's bubble, but Verizon has yet to confirm it will carry ANY specific Windows Phone 8 devices on the release date. They have simply chosen to not deny they will have them. If every "leaked" roadmap was true there would already be a quad-core iPhone, 7 inch iPad, and 10 in Playbook.
With all of that said, claiming exclusivity of anything with AT&T is remarkably stupid and I doubt Microsoft is happy about it. Exclusivity does not work when you are starting from a market penetration of near zero. Quite frankly, leaving all other issues aside, lots of people have left AT&T and will never go back regardless of what device the offer - they same is also true of Verizon, T-Mobile, Sprint, etc.. Forcing them to a specific carrier in order to get a specific device as likely gets many to complain and then choose another device on their preferred carrier. If that carrier is late to the game with Windows Phone 8 devices, guess what they are going to buy? This is the antithesis of wise marketing when attempting to actually grow a market share from (near) scratch.