I too have noticed these. I only buy one way tickets and usually the day of or the day before travel. I am consistantly getting M or lower fares including a one way from LAX to ELP for $135. I don't mind, tust me! But I would have paid for the Y or B had it been the only thing out there.

That said, more of our business is going to UA b/c corporate policy forces most employees to take the lowest fare and UA has been the lowest!