2007mom. The waitlist is not meant to keep people hanging. Think of it more as a deferral. Only when they receive word from accepted students whether they will be taking their place in the school will they know how many openings they will have.
What I would would suggest to all students and parents is if they know they will not be accepting a position at a school that they notify them immediately to make room for others. For example, if student has been accepted to XYZ University and also UNC, and still waiting for other decisions, but they absolutely know that they will attend XYZ over UNC, then they should let UNC know now. I am not saying that this is for everyone, just those that are certain to go to another school with acceptance already in hand. We know that there are many students that have applied to multiple schools (I remember reading about someone that had applied to 15 schools) and have been accepted at their top and second choice EA. If this is the case, then call those schools you will not be going to and tell them, "thanks, but no thank you, please offer my position to someone else." This issue is especially true with top public schools. The superstar students will apply to UNC as safeties or match, and also apply to top private schools with the thought that if I get into HYPS, then UNC is not needed.
The complications come when they are still awaiting for FA decisions from different schools in order to make up their minds. Perhaps this is what we should be pushing. But if FA is not an issue, parents please have your students let the schools know that they will not be attending.