It sounds mostly like they're trying to cut down wait times in line at the airport, as people fumble for credit cards or cash to pay the baggage fees and agents have to make change; if it's done in advance online, then the airport check-in can move faster. I hate the baggage fee in general, but this particular change doesn't bother me too much. I don't always check in online, if I know I have good seats I can't really improve on by checking in early; this policy change would get me to check in online every time.

-- Eric