It is rare for the assigned textbook to have been written by the professor. Even in the exception, professors are unlikely to receive more than a couple of dollars for each book sold, or say $100 for a typical class. That's not a large supplement to a professor's salary, especially given that it takes a year or more to write a book.

I wonder if the person has modded me off-topic realised that one of the winners is a movie called 'Beowulf'!

I agree with you completely. Personal information - your preferences and shopping habits, for example, should remain your own. There is too much potential for abuse, as you've aptly demonstrated. I certainly do not wish to be pigeon-holed by a company because some marketer has decided that it is statistically likely that I fit profile xyz. The area where profiling concerns me most is the online news media. It does not bother me so much that media outlets would like to find out what their customers are reading and with what frequency. When they start requiring me to provide information such as my sex and age on sign-up for their paid services, however, I start to become leery. How long until I start being provided with the "service" of seeing different news than people who fall into different marketing groups?