You are right that the corner cases need some attention, but in the grand scheme of things, I do not see an Olympic Level athlete always putting out exceptional successes no matter what he does, and I don't see someone who has the basic skill level to actually succeed failing all that much. The middle ground is where it does get interesting, and I don't think that I want a difference of 4 skill ranks to be all that glaring in that middle ground.
Degrees of success matter in my games. From easily quantifiable things like who heals more boxes when performing first aid to not just did the con work but does the guard have doubts and or second thoughts. Sadly a guy with a 20 minute class in first aid while in the Boy Scouts performs almost as well a practicing surgeon.