When in a friendship with a member of the female gender, not only do I never ask if she's dating anyone, but they rarely ever tell me. I don't even ask new friends with whom I might feel a certain spark. The point is that I never ask the question, "hey, are you seeing anybody?". That's not because I'm afraid she'll say "yeah", because that way the pressure's off: I don't have to ask her out. I'm more afraid that she'll say "no", in that she's not dating someone, because I'm afraid that she'll ask as a follow-up "why do you ask?". I have no good answer to that other than a truthful one, and you know how that goes.
Call it a Don't Ask Don't Tell Policy, where I don't ask and they don't tell. Some do tell, but they tell me in passing, and when they do, it affects more far more than it really should. It's not so bad when it's the women that I enjoy being friends with and for which I had nor have no romantic attraction to—they're extremely attractive, but I'm not attracted to them—but the one that really got to me was the the girl who I explicitly asked out on a date, who said she didn't date, and then months later mentioned her boyfriend matter-of-factly. Lucky for me that she did this in IM, because otherwise I would have had to make the facial expressions I made after having politely excused myself.
There's little likelihood that this policy will change. Not because it's been working so far—it should be pretty obvious that it hasn't—but because there's no real alternative. Other than a woman making the first move, of course.