Sandflea, actually what i was saying wasn't that i hope they're altruistic (come on dude..no WAY a business is gonna be THAT altruistic). I was saying that they'd be selfish in trying to conserve their yield. as we've heard from lamyers and waiting--THEY ARE. it makes sense too. if a school, say SLU, liked me but thought "this kid's from Miami and they probably interviewed him in some florida schools..he's gonna wanna stay cuz they got it good down there" (especially since my interviewer mentioned UMiami and Jackson hospital like 4 times during our interview), then they might waitlist me, asking waitlistees to call and say they wanna keep their waitlist spot (show interest). if later on they see i'm no in anywhere, they might pick me off the list before they decide to pick off some dude who's gotten into a better school (all schools know where they stand as far as whose probably more attractive to what students--it involves where they rank themselves and how much interest you showed in that particular school during the interview).
Also, if they are thinking about waitlisting me, and accepting someone else from my interview day, but see that he's already in a better school, then they won't "overcommit" like lamyers said..instead they'll think twice about accepting someone else--like me.