I know that if you buy a car out-of-state and bring it in yourself, you're only allowed a 1 year sticker. In '07, I was relocated from Michigan down here, and bought a brand new car literally two weeks before my move. When I arrived down here, they only let me get a 1-year inspection.
My guess is since it wasn't originally shipped directly to the Texas dealer, they may have been afraid that it wouldn't pass inspection down here (in Michigan, we didn't have to worry about emissions, front plates, or hurricanes... just snow
).