I am currently writing a paper on high speed RTOs. I have looked at the different speeds used by Boeing and Airbus (80 versus 100 kts). First these numbers are not certified. Other manufactures have given others numbers like 70 kts.
I believe the 80 kts from Boeing originates from the Takeoff Safety Training Aid (1993). However I am not 100% sure about that.
Airbus gives the following background info on their 100 kts. value.
The statistics and experience have shown that, as soon as the aircraft reaches 100 knots, the safest course of action is for the flight crew to continue the takeoff, unless a major failure or a serious situation occurs.
The takeoff roll is divided into a low and high speed segment. If the aircraft speed is less than 100 knots, the aircraft is considered to be in the low speed segment and an RTO decision leads to a low risk maneuver. If the aircraft speed is above 100 knots, the aircraft is considered to be in the high speed segment and an RTO decision may potentially involve more risks. The speed of 100 kt was chosen to help the captain make his/her decision and avoid unnecessary RTOs at high speeds.
See: www.skybrary.aero/bookshelf/books/197.pdf
Also note that autobrakes often don’t work at the lower speeds during an RTO.