i believe that admissions directors are judged by their schools largely on the basis of simply summary statistics: admit rate, yield rate, average SAT, number of URM, etc. No one monitors these people on the individual file level (as a professor at Dartmouth who was on the admissions committee for many years told me).
I think all schools–other than Caltech–play games to some extent. They have an incentive to do so given how they are judged. For instance, Harvard is notorious for encouraging kids to apply who have no chance at admissions. Why? It lowers their admit rate. Another game that schools play is with early decisions, which are binding, as opposed to early action, which is not. REA is a hybrid. Did you know that over half of Penn’s incoming class is EA? That’s one way to decrease your admit rate and increase your yield rate!
http://www.admissions.upenn.edu/apply/whatpennlooksfor/incoming-class-profile
To Stanford’s credit, they seem to play this game a little less than other schools. (Again, Caltech is the outlier.) In particular, other top schools seem to use the waitlist more than Stanford. There has been a discussion of what the yield rate is with kids offered from the waitlist. I don’t think you will ever see this data, although you can rest assured that all of the admissions offices have them. My guess is that the yield is close to 100%. An admissions office first calls the guidance counselor and says, “Harvard calling. We are thinking about offering Sally admissions off the waitlist. Do you think she would be interested?” If Sally has moved on, say to Yale, the counselor is likely to say no (although in that case why is Sally even on the waitlist). More likely she will say, “Sally really wants to attend Harvard.” She has probably told Sally to write a note to the Harvard admissions staff to that effect. Hence, for a variety of reasons, the yield rate is likely to be very high among those coming off the waitlist. I would not be surprised if some years it was 100%.
It looks like Stanford took 51 off of the waitlist this year. Harvard with a slightly smaller class took 75 off the waitlist. (In prior years, Stanford took no one off the waitlist while Harvard took many.) On the margin, that makes Stanford yield rate even more impressive.