<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by mbstone:
The idea is to charge more for business travelers who are spending OPM and less for leisure travelers who are spending TOM. They figure anybody staying over a Saturday night must be a leisure traveler.</font>
Exactly. Full-Y flyers departing ORD on Thurdsay morning for LAX generally want to depart Friday after lunch to get home Friday evening, not on Sunday morning.
Business travelers generally detest being away from home on Saturday and Sunday, so the Saturday night stay evolved as a fairly good proxy for separating business flyers from leisure flyers.
Nowadays, however, more and more business flyers are willing (forced?) to put up with weekend travel to save a buck (or thousands).