I think in the US, the size and focus of the university affects the campus culture. I went to a liberal arts college for my undergraduate degree that was smaller than my high school. We had no TA's, and the classes had no more than 30 students in them. I would have never called my professors, even the adjuncts, by their first names.
For my professional graduate degree, I went to a huge state university. I had to take a freshman-level course as a prereq before I was allowed to begin my graduate courses, and there were 500 people in the lecture hall! It felt really odd to call the TA by his first name, too. In my graduate program, the unofficial practice was to call anyone with a Ph.D. Dr. Whomever, and anyone without by their first name.