In the end I feel it is fair to say that the criticism of coaches is completely based on expectations. (I hope that isn't controversial.)
The question is are these expectations realistic? It should be noted that there is a difference between "expectations" and a desire for a magical season. It should also be noted that even if the expectations aren't fair, that does not mean all criticisms are not fair either.

Go back to football season: after we defeated Texas in week 2 some crowned Hill the Heisman. We even had some who hyped us as a potential playoff team. In basketball we have had a few good seasons where we were absolutely spoiled making it relatively deep into the tournament. This year the tourney isn't out of the question yet.
It then seems like falling short of the above or "the magical seasons" sets coaches up to fail.

I don't understand the almost bi-polar nature of some fans. There are criticisms that can be made of both Bronco and Rose- I bet they'd both admit that. I just wonder if some go further than justified in criticizing either coach.