Great point. I had a friend who worked as a salesmen at Thomson West when they still owned Thomson Learning which published all their academic materials. To say the industry is entrenched is an understatement. My friend told me once a publisher was in with a university, there was virtually no way other publishers could get in there. Even the professors had little or no say who they could buy their books from.
That's weird to hear. Lots of professors use their own textbooks in their undergrad and (especially) graduate classes (e.g., Yaser Abu-Mostafa uses his own textbook for http://www.work.caltech.edu/telecourse.html).
Also, there are certain canonical texts that are used almost universally across all universities during a certain time frame (say, the CLR algorithms book, or the Cover and Thomas information theory book).
It's a few steps removed from organized crime.