When athletes go faster it's the stride length that should increase, not the stride frequency. I don't believe it's possible to get your stride frequency beyond a certain threshold. Even the world's most elite sprinters don't try to make their legs move faster, but rather they try to produce more force with each step.
The same applies to distance running. When you speed up from a 8 minute mile to a 7 minute mile, you probably don't take that many more steps, but instead try to make each step go further.
I'm no elite runner or anything but I think the whole 90 cadence/180 step thing is a little overplayed. It might be helpful as a rough guide when learning how to adjust your running pace, but I don't see the value of it beyond that.