I have just realized that the B757 can be ordered with two exit types.
#1: 6 main doors, and 2 small exit doors behind the wing
#2: 6 main doors, and 4 overwing exits (737 style)
Airlines like FI and BA use the first type, and airlines like UAL and DL the second type.
I was wondering why the 757 has those exit options.
My guess is that FAA "order" american airlines to use #2, because that means more exits. But I don't know.