There's so much more than hp #'s. Not only is the info quoted below a reason but for other reasons, as well.
Driver
Usable hp, ie; traction, power curve/torque curve
Gearing - transmission, rear end, tire size
Auto vs Manual
Weight of vehicles
Suspension setup
Whoever got the jump first helps obviously
Every single thing that happens physically when you hit the gas is due to power from your car. This includes even the flex of your suspension, bushings, frame flex, motor mount/motor movement, etc. Every little bit that doesn't go to the pavement or is being used to put said power to the ground is a waste of power created by your engine. Of course, now we're getting into smaller shit. Anyway, there's just so much that goes into it. This is just off the top of my head. This is why letting someone know your hp isn't neccessarily showing all your cards.
Oh, let's not forget the guy said the power was easily adjustable given the race he was in. Nice thing about boost and/or nitrous.