I'm going to post comparisons for 1 episode from each of the first 3 seasons. I'm confident there's no major cropping involved. Especially after doing the comparison for the Pilot not too long ago, and there's no cropping at all. There's actually more at the top.
EDIT: Comparisons for S02E15 "Marie's Meatballs"
I know it may look like they're cropping a little on the bottom, but they're not. It's just re-framed slightly, easy to see when you look at the top of the frame which has more than what you see in the original. So far the only scenes I've noticed cropped are the outside shots of their houses. Also, can't compare the opening credits. They used a completely different take.