That is an extreme case – I know which people in my office have “significant others” (and have met most of them at social functions) and which people are completely single, but everyone does talk about this much less than Americans. And to give another extreme example, one of my students told me that he was really busy but that he had a European vacation coming up soon, and he talked with me for some time about his trip after he got back, but never mentioned to me that he was so busy because he was getting married and that the vacation was actually his honeymoon! He didn’t even say anything about anyone else going with him to Europe. I only learned of the marriage a week later when one of his classmates (who worked for the same company he did and had known him since college) made reference to it.
On the other hand, I’ve had people I don’t even know very well ask me personal questions about my romantic life that I’d normally consider inappropriate from anyone but a friend during a girl-talk session. I think part of the reason for this is that the Japanese are aware that Westerners aren’t as discreet about these things as they are – but they don’t know where we draw the line. But one of my more advanced students also explained that for people who want to make conversation with fairly basic English skills, “Do you like…” questions are very easy to make. So they may start grilling foreigners about their personal preferences in all areas just because they can’t think of anything else to say in English.
Lamia: This is why it’s interesting to compare experiences with other foreigners; you learn things. I’d only heard little girls using boku and very occasionally ore and I thought it was just a kid thing, like they hadn’t completely figured out what the social conventions were yet. I haven’t been able to hang out with fringe groups in Japan because I live in the countryside where it’s pretty conservative so I’ve not learned much firsthand about the homosexual community. I agree that both those cases were extreme, and I also think your reasoning about unexpectedly intimate questions is sound.
Utena in Revolutionary Girl Utena (who is portrayed as bisexual and quite butch, with a thing for cross-dressing) uses the masculine pronoun too. She actually says at one point “Boku wa shoujo desu” (if I have that right,) which is basically “I [masc] am a girl.”