Well, pianists are a strange kind. We stay in practice rooms all by ourselves for hours and hours, thinking about playing the music to perfection, and how to reach that goal. Do you think this changes our social behavior? I cant help but think that one becomes so much more self-aware, to the point where interacting with others doesent have the same effect as it used to. Its as if i think and work so much with music and what it gives me, that nothing else has the same value or interest. And relationships feel different as well.
Or maybe its just me. 
I think this has to do with accomplishing goals, and being able to call it a day. If you are always practicing aimlessly, hours on end, it will hurt your social life because you won't know when to show off your personality, and when to invest all your energy in obsessing over music. There is a time to reap and a time to sow. Many pianists cannot "turn off" so to speak, and many choose not to, but those tend to make unpleasant or even nonexistant impressions in social settings.
Also, those that can't "turn off" and spend their whole lives, either physically or mentally, in the practice room, often have a sense of entitlement, that they deserve accolades, performances, attention, and respect. In the practice room, they inspire themselves by imagining themselves to be on a grand stage, in front of a large, cheering audience. They don't realize how much of that comes not just from having skill and talent, but from being able to give of oneself and inspire others. As a result you see bitterness and pessimism rather than optimism and generosity. I don't mean generosity of the purse, but generosity of the emotions.
So many great pianists have also been, and are, great
raconteurs - Rubinstein, Gould, Gavrilov, Richter, Busoni, Hofmann, Cortot, Fischer, and so many others were known for their power of conversation. They knew how to say, enough work for the day, now we can enjoy the company of others (or, "they can enjoy the company of me."

Recently the young (28) head of the organ department at Juilliard, Paul Jacobs, gave an interview in the Times in which he described the almost total lack of human relationships in his life. This cannot be good for the soul, or for music-making. Anything which becomes isolated, also becomes suffocated and stultified. Bartok discovered this when he researched the music of North Africa - it had been out of touch with other civilizations for generations, and never changed, never developed, and, compared to the other folk musics he studied (with similar origins), was not interesting. It's of vital importance for a musician to develop social skills.
Walter Ramsey