I think it depends on the program and how much funding they have. Speaking with the profs at ND yesterday they expect to be able to accept 10 students from those that visited, but only offer spots to 10 at first even though they don't expect 100% matriculation. Programs don't want to admit more than they can actually fund. That being said, it is my understanding that everyone in attendance at the visit day is on the short list (not necessarily the waitlist), and I noticed earlier in the month someone claimed a waitlist at ND. I don't really know how that factors in; I figured that those who aren't offered first round acceptances will be waitlisted, but this might not be the case.
All of this is to say, there are probably different institutional logics at play when deciding on the strategy programs use for acceptances and waitlists.
