I have always been interested in what the seat pitch was when this rule was first implemented. I imagine it was way back in the first days of jet travel, when the seats were at a 35-38" pitch. With that seat pitch it's not such an issue, but when they cram the seats in at 31", then it's a whole different story.

When you're 6'3" and the seat pitch is 31", there are not many options regarding that precious space - that room under the seat in front of me is where my FEET have to go. Restricting that space actually makes me have to put my feet behind my knees, which means sitting in a position where my heel does not quite hit the floor. This is REALLY uncomfortable after a short time, and results in a very cramped ankle and toes. It's just an un-natural position.