I suppose the biggest losers are, as you said, the occasional flyers, especially when they're hit with things such as checked bag fees that the Elite are spared. Corporate travel budgets could be losers if people focus business on "their" airline or hotel to the exclusion of cheaper alternatives. My company monitors whatever you choose vs. cheaper alternatives, but my manager is happy as long as I have an explanation and the difference is reasonable. (Examples: not taking a 7 AM Sunday flight out after getting in from London the previous Friday; not taking a flight with an average delay of 55 minutes to make a 30-minute connection at ORD.)

I qualified for Platinum on AA last year but also flew DL, WN, NW, AirTran, Midwest, Jet Airways and Swiss. Whatever makes sense.

I'd say Southwest takes good care of everyone. Their FAs actually seem to like their jobs. Despite my AA status, I just chose WN to fly to Chicago because their schedules were better. Yeah, I might get stuck in a middle seat and AA MIGHT have upgraded me, but I'm taking an 8 PM flight home and I trust WN to get me there on schedule.