[mturmon]

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).