I was waitlisted last cycle, starting at number 132 out of 141. I wasn't pulled off the waitlist, but after the class had been decided around August, I was offered a deferred admission over the phone by the new dean. He didn't elaborate on how the decision was made for who was offered a deferred admission, but it must be something besides actual waitlist ranking.
For stats, i had a 3.0 undergrad, 3.6ish masters (all med school classes/lab thesis), and a 32mcat (13V, 8P, 11B), plus the usual assortment of work/volunteer/shadowing that everyone else has.
A deferred acceptance is not an early decision, so I am still applying elsewhere this cycle. As for turning a regular decision into a deferred decision, I believe it must be along the lines of a medical/family emergency that prevents you from attending school that year, not something like squeezing in that backpack trip to Europe you've been dying to do.