You know, I've thought about this a lot, and I have a theory.
I think med schools don't really have a simply-ranked waitlist per se. I think what they do is that they try to pick a person off the waitlist who most closely matches the person who just came off it. Lost an athlete from the midwest? Try to get another athlete from the midwest! Lost an international student? Try to get another international student? Lost someone with a 42 MCAT? Try to get another high-MCATer! For that reason, to say your exact spot on the waitlist would be kinda pointless, cause while you may be the number 1 half-Japanese liberal arts major from the south, it's not really guaranteed that the other half-Japanese liberal arts major from the south will drop out, even though maybe a good 30 people will drop out of the class in total. I think that's probably why they give vague "tier" classifications.
On the other hand, I do wish that every school gave those tier classifications, and that they wouldn't use BS feel-good terms for them (I'm thinking of Penn- tier one actually means tier 3, since there's a "top of tier one who goes to second look", and a "top of tier one" and then a "tier one").
Edit: as for me, I had 6 interviews, 3 acceptances and 3 waitlists.