I guess I had a different definition of "advantage of applying early."
For rolling schools, the sooner you were reviewed by the committee, the more interview spots and seats are available to you as an applicant. This "advantage" was just a byproduct of the sheer number of applicants to seats ratio, not some advantage that the schools intentionally created.
However, not everyone who interviews in February/March/April applied late. That was just when the admissions committee decided you were worthy of an interview based on their seance and ouija board readings.
I also understand that a school could fill up it's available number of acceptances prior interview season ending. It would be nice, if that was the case, that the schools would let you know that you are, in fact, interviewing for the WL.
To get back to my original point, it's curious to me that they would pull from a WL before having all available candidates for the WL. If I were on the admission committee, I would want to wait to see all the candidates on the WL before I started pulling from it. Obviously I'm not on the admissions committee and they are not following my logic. I was just curious if there was some other logical explanation, but I doubt we'll ever know what goes on.