Yes it's a liberal/progressive thing, but you're dealing with academics. The majority are going to be liberal, like it or not.
Regardless of politics, though, I think the reasons above better explain why more and more people use the term partner both when referring to their own partner and when referring to others' partners: you can't assume everyone is straight, you can't assume everyone is married, and using a term that is more often limited to straight couples (husband, wife, although some homosexual couples do use these terms too) can ostracize others who do not use these terms…
Also consider age and relationship status. For example, I am 32 and I have a girlfriend who's also 32 and also a professor. Are we boyfriend/girlfriend? That seems so junior high. So, another term seems better. "Partner", although giving off a homosexual connotation which could be misinterpreted, does portray our relationship as more stable and more committed than when a 32 yo man says he "has a girlfriend". So, some people might choose to use the term because our society does not have another term to describe two non-married adults in a committed relationship. I guess "significant other" could be used, but others still might assume you're referring to a same-sex partner, which some individuals might not care to portray.
I might start calling my girlfriend my "womanfriend" ("ladyfriend" sounds like a casual-sex partner).