I really like the ads, even before I got an iPhone I always enjoyed seeing the ads, especially the pilot one and the vacation one.
And about AT&T, Apple picked the most popular network in America (18m more than Verizon, 67m vs. 49m) as well as the most advanced technologically.
Plus, without making an entirely different model it could only have been used on T-Mobile, which doesn't even come close to AT&T as far as coverage is concerned.