The waitlist may be several hundred people long, but consider this:
Let's assume that their admissions schedule is roughly the same for each year. I.e., offering 1/7 the class every month.
By the end of the seventh date, enough offers have been made to the entire class. Since their class is ~300 people, you would expect ~300 offers.
However, if you look on previous pages of this thread, not only do they interview more than 300, they also admit more than 300.
This is to compensate for people declining admission offers. In 2008, 754 people were interviewed and 588 were accepted. Many of those must have come from the waitlist, so even if the waitlist is a couple hundred people long, a considerable number of those couple hundred are going to end up being accepted.
Hold tight, people.