Sorry, that Hunnybear post was actually from me. Yes, United is annoying that way in that even if you already own a W seat, in order to qualify for the fare guarantee the W fare class (or whatever you're booked in) must have ANOTHER seat currently available. It kind of makes sense in a way but it's stingy of them.

I've been noticing that United seems much tighter with their yield management, especially LAX-LAS, than the competition and as a result I've been flying competitors on that route who consistently have lower prices as a result.