Tom,
Sorry to delay with a response, but I've been out of computer range for a while.
Admittedly, most of my work is not in resort type courses. Also, I will say that in the case where a particular course in a multi-course facility has a lot of recognition, such as national ranking, that also skews the results. However, when it is your basic local play course, particularly daily fee, the results seem to be similar. The usual response I get from the head pro is something to the effect that "our older regulars don't like to get beat up, they just like to come out and have fun". My most recent experience is as the CFO of a multi facility operation. We had two 36 hole operations, and the easier of the two courses at both facilities got the heaviest play. In these cases, they were easier primarily because they were shorter, so that may have had an effect.
My sense in most cases, however, is that the more difficult course in a 36 hole facility will usually have more difficult green surrounds and more veritical bunkers. Older folks can't get around these as well with bad knees and such and start to dislike them.