kawasaki
I ranked Yale 3/4 and was dinged without interview. I was waitlisted last year when I ranked them 1/4. So in a way, the rankings do play a part in their decisions. It may not be the sole reason, but I'll argue that it sure has part to play. In my opinion,
I was good enough to interview last year, and be placed on the waitlist, and mysteriously this year I wasn't even good enough to get an interview??? Either ways, congrats to ALL of you who have been admitted. You definitely deserved and earned it.
Sure, your ranking could have had something to do with that, especially since in adcom's eyes they were your #1 choice last year and this year they dropped to #3. What leads them to believe that you'll accept their offer this year if you don't like the school as much anymore?
Beyond that, this also comes down to the applicant pool. I know Soojin at Ross has a blog post about this very topic, but getting WL-ed or accepted last year doesn't guarantee another WL or admit this year. Every year, the pool of people applying is different. Perhaps more people this year have a similar background to you or have similar goals to you.
There are a variety of factors that go into the decision-making process; from an applicant's point of view, you can't quite understand it (and in some ways, you think you've gone "backward" over the past year), but from the adcom pov, they're just trying to make the best class they can.
Best of luck with your other applications & congrats on your admits so far!