From what it seems like on the trail, is that getting an interview pretty much qualifies you for the residency program and the interview is meant for them to make sure you're not socially inept and also let us get a feel for a program.
I've had similar instances of programs telling applicants a) we've all probably applied at too many places, b) we're interviewing at more than enough places, and c) a majority of us will get our top 1 or 2 places on our rol (I'm sure assuming we don't rank places we didn't get interviews at).
I'm guessing what the OP is wondering, which I've also wondered, is if this is really the case. It makes sense because I think a lot of us look for and weigh different things whether it be location, reputation, research, etc so everyone's top ranks are diverse enough that a lot of applicants can get their 1 or 2. However, it's can't hurt to see what the "evidence" whether it be skewed or not (hopefully since it's anonymous it will be minimize that).