I would err on caution contrary to what's being posted and say you should assume you won't get off the waitlist. It's definitely possible, but the odds are against you and it's better to play the probabilities and assume you're not getting then (so if you do, you're delighted, and if you don't, you're not disappointed).
While many applicants are cross-admitted and necessarily must decline schools, schools also try to account for this by overadmitting by as many was 4-5x their expected matriculating class. So often, a few people slip through the waitlist, but it's definitely not as frequent as you might hope and you shouldn't count on it.
Play it safe and go with what's certain. If you're on a waitlist, plan for not getting in. You still might, but don't hold your breath.
