True that, but the gate was located in bottom of a missile silo. It would have taken quite significant changes in the silo to allow larger vehicles in and out without much hassle. The whole concept seemed to revolve around to prevent probable invaders from getting outside and protecting outside world from any sort of catastrophe. Stargate Command probably could have avoided many losses if they have had proper vehicle support when situation warranted it. Heh, it would have been way outside of a tv-series budget, but proper warfare between SG and Goa'uld would have been real nice to see.