I know certain schools do give out more acceptances, but highly unlikely twice as much as the actual class size. For one, Medical College of Wisconsin does give out almost twice as many acceptances as seats right off the bat. I'm not completely sure about other schools. Usually, during orientation, don't they tell you? I know for several schools I interviewed at, they told us how many usually gets off the waitlist.
Also, a lot of people reserved seats up until the final day to make a decision, so theortecially, a good portion of those seats become open to waitlisters in May. Of course, I'm just citing anecdotal evidence. Not sure if this is really teh case. Best thing to do: call the individual schools you are interested in.