re: Why can't college football have replay booths on the field?

Actually, it's BETTER to have a replay official and take it out of the hands of the guys who made the initial mistake.

What both college and the NFL SHOULD do is something similar to what they do in rugby. On a close call, the referee signals up to the booth for review, and simply asks, for example, "Did the player touch the ball down in the try zone before or after he went out of bounds?" The replay official reviews the play, usually very quickly, and responds either with, "Yes, you may award the try," or "No, the player hit the flag and was thus out of bounds prior to touching the ball down."

Very simple, clear cut, eliminates the coaches from it, and gets it right. No ref having to run over to the sideline and ask for various angles.