I would assume that there are a certain amount that really aren't all that stellar. I mean if you are qualified for GS and want to do plastics, why not give it a shot? Maybe a shot in the dark for some, but worth it. Worst case scenario you take a GS slot and try again later for the fellowship.
As an example that may or may not back up my point, I read on the Wake Forest site that the average applicant last year had a 220 step I. That seems to indicate a lower level of achievement (at least on step I) than might be expected. The way some folks talk, you'd think everyone that applies has a 250.