I'm jumping right in after reading just the first page of this thread, so this point may have already been made.
Aren't these wrestling/BJJ stats more to do with the fact that wrestling training and regular competition is offered at high schools across the US, whereas BJJ instruction is expensive and harder to find outside sizeable cities?
Not wanting to sound like a BJJ nutrider, but it wouldn't surprise me at all to find that a huge number of professional fighters had been on school and/or college wrestling teams. That's not the same as saying that wrestling is more important or useful for MMA than BJJ. It's just saying that (whilst undoubtedly useful) the wrestling was much more available to young atheletes all over the country.