After seeing this thread I went and tried on my old 32x32 jeans. Amazingly they seemed to fit just fine! Very odd. However they were a little bit too long for me before. I think I was actually a 31 length pre-surgery, but that's not always an easy size to find.
LAGrowin is definitely right about the glutes, hips, and thighs helping to fill out the jeans. I think once I gain those back, they will lift the bottom of the pants up and I may need a 33 at that point. I think we may also subconsciously be trying to wear them a little lower on our hips than before, to make the torso look longer. That might explain another 1/2" or so.