@neil for me personally it's a manifestation of claustrophobia. I need to be able to get out of a place quickly. The same reason I won't sit in the back of a 3 door car or in a window seat on a plane. Too many barriers = panic attack.
It's estimated 5-10% of the population have claustrophobia, so if less than 10% of the seats are end seats, then that might explain why it appears that there are a large number of 'hoggers'. ;)