The 80 kts technique is an old one that seems to have survived somewhat. At 80kts when throttles go into clamp mode and that seemed like a good time to match a Go-Oriented decision point since we call "80kts". Honestly, the C-17 like the C-130 is very stop oriented. Even if we had several blow tires, some hesitation, and a Great Dane or two in the back, we would not have any trouble stopping on 90% of the runways we operate on. It is still good to talk about though, since certain emergencies can affect your stopping power and can cause you more trouble trying to stop rather than go.
I like the FAA and Boeings recommendation of 100 kts, but still we have plenty of excess stopping power. One thing that needs to stop in the C-17 community is the negative press blow fuse plugs get. If you have a high speed abort and blow your fuse plugs, that is a good thing. That means they worked. Seems every time I hear someone blew a few tires, everyone thinks they screwed up. Well, sometimes they did... riding the brakes, landing without checking your brake temps after a recent takeoff, ect. However, I am afraid someone is going to go light on the brakes because they are afraid of blowing fuse plugs and end up in the dirt.