Oh, I know that ... and I wasn't directing that comment at you in a pejorative way at all .. I was just pointing out the realilty of that concept.
Yep, me too, and I think it's great! That said, the web is NOT such a place, and by definition my not locking my doors means I'm not practicing "security" of a certain sort (there is the gun in the night stand, but that is another matter altogether!)
It's really hard to tell; my experience has been mixed. As has already been mentioned, there is referrer information to consider (if you ever browse to another site from that subdomain).
No, it doesn't but there are other tools out "in the wild" that can (think reverse DNS tools, etc.)