This seems to be a common strategy more generally. It appears the tactic of using last-minute letters and emails requesting interviews and essays to determine if people are serious is more evidence that schools are getting frantic about carefully screening applicant pools.
Now, it is not sufficient to simply meet a school's standards, but you must be absolutely set on going if its one of the 'just outside the top 5' schools that has an inferiority complex (ahem, Northwestern and Penn).
The tremendous numbers of holds/defers and waitlists is just another sign of the way this admissions process is becoming out of control.
I suppose its pretty much all due to US News and World Report that schools have to be so careful and take eons to make choices. So, since we are all probably the first ones who will buy the Grad school edition of US News in April, we are probably at fault, too.