This is a good point. When I went to the Indiana University orientation several of the OT students who helped with the orientation also received their spot from the waiting list about 2 weeks before the program began. At their program the admissions director said that they usually go 15 people deep into the waiting list because people's lives change all the time up until the program start date.
However being on the waiting list has to be so stressful since you don't know when you could be called. One of my friends had just moved into an apartment at Purdue when she got the call that she was pulled from the waiting list for one of Ohio State's medical programs which would be in state tuition for her. She packed up and went. Talk about last minute!