Moebius Stripper, whose blog is unfortunately defunct, wrote back in 2004 about course descriptions that describe. She points out that traditionally, course descriptions of mathematics classes are ridiculously uninformative and basically boil down to transforming the table of contents of a textbook into a run-on sentence. And then we wonder why students see math as a bunch of disjointed pieces of information with no overarching narrative to tie them together... don't we come into the classes with that attitude?
See, for example, my institution's mathematics course listing. Physicists do the same thing. Historians, for example, don't. People in the English department don't do it too much, although one does find the occasional list of books to be read in a course description. I am not sufficiently interested in this question to systematically study it, and even if I were there are other more interesting things to study first.
I'd heard this idea before; I'm not sure if I had it originally, if I got it from Moebius Stripper back in 2004, or elsewhere, but I know I think it every time I read course descriptions. Fortunately I will never be reading course descriptions from the point of view of a student taking courses again. (For those of you who don't know, this is my last semester taking courses. Today I was on campus and saw a pile of Fall 2008 course timetables. I almost took one. Then I realized that for the first time in many, many years, I will not be taking classes next semester.)
This may have something to do with the fact that it's expected at most universities that students shopping around for "elective" courses that they don't know much about are probably going to take more humanities-like classes; I don't have hard data on this, though. There's less of a point in trying to craft a good course description if you figure that nobody who's reading the course catalog looking for something to take will even look in your department. In fact, I don't even have anecdotal evidence for this claim, because I went to MIT for undergrad, and the normal rules don't apply there.