"My guess, without knowing, is that they will check your ticket when you board and if you aren't in the proper class of service, if you take aboard a rolly bag for instance, they are supposed to stop you and make you pay to check it."

I would guess there won't be any overhead bin space available if these folks are the last to board.
It always amazes me the amount of stuff and the 'oversized' carry-on/suitcases people bring on the plane. <img src="http://www.traveltalkonline.com/forums/images/graemlins/duh.gif" alt="" />