My two cents:
HK, you're absolutely right that there's no reason to be taking 100 level courses for content you tested out of in advanced HS courses. I bet he's in for a different experience, when he starts taking upper level courses in his major!
I have to quibble with your assertion that the volume of an advanced high school student is greater than college. Bear in mind that generally, the high school student gets a whole academic year to cover the material in a one semester course at a university.
An example from my own life, I took AP Calculus and passed the AP test as a senior in high school (I had an honors/AP-heavy course load that senior year). It allowed me to test out of a college math course, but I still needed math credits for my major (Geology). The pace of my Math 111 and Math 112 courses was much faster than anything I had experienced in high school. The same goes for other "college level" courses I took in high school; we covered similar material with similar assignments and evaluations, but we took twice as long to do it.
In my experience, most of the courses I had for my major in college were much harder than anything I had in high school, but many of my GE courses were on par with or easier than my "college level" high school courses.
