<p>We don't know the history -- how many waitlisted WU students accept the spot. If WU is frequently used as a backup for Ivies, we can safely assume that no student ever admitted to an Ivy accepts the waitlist spot, for example. So it may be that historically WU has seen a huge attrition with respect to waitlist spots. There are also probably a lot of strong candidates who apply in hopes of receiving merit aid who won't bother if they are waitlisted, since a WL is a strong signal that merit aid won't be available.</p>