I am generally always one of the last to board, generally because I hate waiting in lines. However think of this very real situation which has often happened to me at some airports (mostly not UK):
I am last to board, I go down the steps and realise there is a shuttle bus to the plane, with everyone waiting inside! Since I am last onto the bus... I am closest to the door and hence first off the bus and first on to the a/c!

Now you are paying a fiver to be last!