The seemingly unrelated questions have to do with testing you basically. They're just trying to see if there's any unusual hesitation, or unusual answers, that would seem suspicious.
Even before 9/11 they were cautious, nowadays even more so.
And there's quit a difference (in general) in how US Customs and Canadian Customs go about it isn't there? I've found that in general US customs is much more abrupt, almost scornful of travellers. The odd time I've had an agent that was pleasant and ONCE I had one that actually smiled at me! I'm sure he didn't last long. Canada Customs tends to be a little more matter-of-fact, almost bored. Unless they're in suspect mode, in which case all bets are off.
And what about the security screeners at the airports? Since 9/11 the worse screenings in terms of actual security that I've had to go through have been in US airports. I was in Las Vegas in November '01 and thought that security would be brutal - it was a joke. I walked through the scanner and it was fine, but they decided I needed a secondary hand-scanning anyway. I was told to go "over there" but there was no obvious place to go. I moved a little in that direction and just kinda stood there, and after about a minute an older gentleman with a hand wand came over, pointed it at me, and THAT WAS IT. He didn't even actually scan, just pointed it. I was on the one hand amazed, and on the other hand disgusted that THIS was their "heightened security".