The NFL is 100% a QB league right now. A premium is placed not just on the QB position itself, but guys that can rush the QB and guys that can protect the QB. A QB, OT, or DE may be drafted before some guys at other positions who are rated slightly higher. And among those positions, Barnett seems to be our safest bet. Maybe Kongbo, if he can live up to the hype (or is he even eligible for next year's draft?).
Edit: I just looked it up. The last overall #1 pick who
didn't play one of those three positions? Keyshawn Johnson in 1996.