I could swear the policy used to be that you had to check in 30 minutes prior to the flight, had to be at the gate 15 minutes before the flight or lose your seat assignment, but that you could board until 10 minutes prior to the flight.

I once had an Eagle flight leave the gate at least 10 minutes prior to the published departure time. I was incredibly annoyed, given that I was at the gate 10 minutes prior to departure. (and hadn't fooled around..my inbound was late)