I'd imagine that a good fraction would actually start to tire (a bit) of the repetitiveness of describing their research hundreds of times over, and would probably want to talk about something else.. After all, does the professor usually benefit when they talk about their research to a random undergrad?
Yet, "ask the professor about his research" is generally considered to be standard social advice in academia... (after all, people love to talk about themselves - http://medicalxpress.com/news/2012-05-people-brain-scans.html ). Is the pleasure of talking about your research similar to the excitement of having the liberty to be self-centered and to talk about yourself?
But maybe professors would prefer to talk about something else - it's just that it's hard to think of a topic that they would prefer talking about, so it's simply a "safe option" to ask them questions about their research?
What I am really interested in - is this - would professors usually prefer to talk about something other than their research, if some such common topic could conceivably be found?
Two points from experience (as a student):
- Don't ask/talk about something that can be googled
If you want to talk about the professor's research interest, that's great but the key point is not to talk/ask things that can be answered in a Google search. Asking a professor about his research interest might qualify as one of these cases. Checking his webpage (if updated) might answer the question. "Why did you use X instead of Y in your paper titled Z" might probably be a good question to ask (depending upon the occasion). Now that I reread my answer, I feel professors are like SE sites. Ask closed non-google-able questions while showing interest and initiative and you will have a good time.
- Gauge the occasion
Needless to say, meeting a professor for the first time in an orientation party, conference or a course orientation might call for different "first conversations". Don't force what you want to talk about on the professor. (But then, this is true for all people not just professors.)