Why do they bother interviewing for the wait-list? Honestly, because they have to. Because most schools send out acceptances throughout the year, applicants (the lucky ones, at least!) can be accepted at one school in September and at another in April... or in July. If School A accepts you first and you get good news from School B, your first choice, later on in the year, that frees up a spot at School A... which may be the first choice of someone accepted by School C, which in turn frees up another spot... and so forth. This happens through July, and any school that ignores this fact will have a much smaller class size than anticipated.
Interviewing for a wait-list isn't very exciting- and let me just repeat that I don't know if that's what's going on! That's something that I read on the boards, not heard at the school- but it's still worthwhile. A wait-list letter from SOM means that they like you, they like you a lot... but that they don't quite have the space- and that's something that changes throughout the year. Everyone hates wait-lists... but it's much better to be on one than to just be rejected out of hand.
Bests,
Paige