Your answer seems to be the best explanation so far, but the Libs will just say that it cannot be proved that they would of passed the CSRT. Or they will say, Why didn't he go through with the CSRT to make sure.
Bottom line: Bush released people of whom the left would say: "There was no hard evidence! It was all circumstantial!"
Whereas Obama has released self-admitted ranking members of the Taliban and Al-Qaeda hierarchy.