I think it was ridiculous that they made "Warp 10" some transcendental state where you're everywhere at once...as if they somehow "knew" that when they were creating the warp speed scale.
Why wouldn't they know? In the real world, we use the speed of light in much the same way. Or with temperatures, we know that zero Kelvin is the lowest possible, even though we've never achieved it. The scale is built around the theory.