Really? I dunno--I always saw employment as more of a business transaction, and I don't give a damn about the personal lives of those I do business with.
Well, that depends. 40 hours a week out of 168 is less than 1/4, but it's certainly true that you spend at least half of your weekday, waking life at work. But more pertinently, it should be time that's set aside for work. I don't know why what we do outside of work should even be a factor, or why I should have to share the cultural values of my coworkers. It comes dangerously close to discrimination.
Well, I think communication is affected by personality "type". So people more "similar" communicate more effectively. If someone is not comfortable talking about anything except work, that says a lot about that person. If what it says is good or bad is another question, but to me it sounds like a boring human being ;)