Yes, my first point was more an observation than an argument; there's nothing really more than that.
Regarding your response to my question, I don't think the fact that a school is a top 20 or not will necessarily, in itself, have that much to do with how the school views waitlisted candidates with or without multiple acceptances. Although, your reasoning is logical and very likely the case in many instances, I don't think that in and of itself makes it necessarily true. For example, candidates who are accepted to HMS are probably also competitive for many other top 20 institution. Admittedly, HMS is probably the exception, since their yield is so high. I agree though, I think it's probably the case in many instances that if a candidate accepted to mid or low tier schools and then is offered a seat at a top tier school, s/he will attend the top tier school. However, if the candidate is accepted to top tier schools and then is offered a seat at another top tier school, what will happen then?
Then I should probably clarify my question further.. how does a school view waitlisted candidates who either have or have not been accepted to multiple comparatively ranked med schools ("multiple" being 2, 3, 4, ...)? They would need to extend a lot more offers to the group with multiple accepts compared to those without any. Do they really take yield into account or would they make these decisions independent of multiple acceptance status? A hypothetical waitlisted candidate with 10 acceptances at other schools will very likely not attend the school that admits them off the waitlist, assuming cost, school ranking, location, etc. are not factors. It would just hold up the acceptance process.