Based on my experience at University great teachers who push and challenge students are generally disliked by the large group of students that don't particularly want to be pushed or challenged.
I think it would be interesting to know if professors who push and challenge within a non-dgree open online course would face the similar wrath? I'd bet not.
Um, have you been to a university? ;-)
When you think about it, the professors aren't (necessarily) there to teach either. They are there primarily for the opportunity to do research though that may be changing as many professors are part time minimum wage contractors.