Yes, Rush's problem is that he never gets to the foul line. In fact, as a jump shooter he's very efficient. Compare his efg% on jump shots (46.9%) to the much discussed Michael Redd (47%). Of course Redd's efg% is more impressive since he's creating his own shot more often but 47% on jump shots is decent. It's not fabulous though. Contrast it to James Jones who was at 58%. Still, for the min., it's not bad.
Rush's problem is that he never ever gets to the line. He attempted 42 TOTAL free throws last season.