[Drunken F00l]

I don't see any of the maps being open enough to put that 20 unit difference into play.

Shows how much you play TF2. Here's another example in case you didn't like the first: Pyros.
For the dense:
The 20 unit speed difference is enough so that the pyro can't catch you even if he cuts around corners slightly better than you. You can use this to your advantage and lead the pyro into his death because his name is OmegaZero_Alpha and he thinks that he runs the same speed as you.