As the top of the draft (going off of DX's mock - Lillard is the first thing resembling a PG taken at #10) is pretty sparse on PG talent, or at least combo guard talent, perhaps Ainge thinks he can move into the top 10 with Bradley.
Either that or we're considering a Pierce move (Golden St. is a pretty logical destination - their Jefferson/Wright/#7 package is only a little inferior to the Wally/West/#5 package that got us a 32-year old Ray Allen), or even a Rondo move (doubt it).