Cause DFW Texas is boonies.... Only the 4th largest metro area in the United States.
I live in Dallas and AT&T has been good for me for the last 4 or 5 years. During the last 2 and a half years, I also spent 19 months traveling 4-5 days a week, all over the country, and generally in a different city/town every day, and AT&T was virtually always reliable - sometimes more than others obviously, but nonetheless, I was never one without any service at all, except a few times driving through the mountains in Cali (but I'm not sure if any service would have worked there). Any cell phone service is going to have its moments where it loses a call or doesn't have the greatest connection.
Case in point - just yesterday, my fiancee and I were sitting on the same couch with less than a foot of space between us. I had full bars on my iPhone 3GS (AT&T) and she had no service on her LG Ally (Verizon). There have been other times where her reception has been better than mine when we were standing/sitting right next to each other.
It varies based on so many things that one company is never going to be 100% perfect in all locations. And one service (especially in larger, metro areas) won't necessarily always be better than another service at all times either.



