Dont Hang,
The reason is that, particularly in large aircraft, a go decision has proven to be the safer option for almost all emergency situations even if, theoretically, you COULD stop on the available runway. High speed rejects are very serious manoeuvers. If the aircraft will fly it is virtually always safer to takeoff, circle, and land thus having the WHOLE runway to stop on, rather than just the bit left after V1.
lomapaseo-
V1 is not a rule, it's a guideline for judgements.
It most certainly IS a rule according to the Ops Manual I am LEGALLY REQUIRED to operate in accordance with. As Captain, I do have the right to work outside the laid down procedures if it is necessary, but that means something has happened so that I CAN'T continue the takeoff.