Specs aren't the same. While processor, HDD, RAM, and screen size (physical) may be the same, there are many differences. The A-Series ThinkPads have up to a 1600x1200 15-inch display, while I believe that the T-Series maxes out at a resolution of 1024x768 (last time I checked). The A-Series is also larger and heavier than the T-Series since the A-Series is desktop replacement, while the T-Series is high end portable, but not desktop replacement. The A-Series also has S-Video in and out ports which I don't believe the T-Series has (could be wrong on that though). If you check out the in-depth specs directly from IBM you will find several other differences as well.
ZV