I think the second part of your first question actually answers the first - a large number of the potentials never know they are, so when they haven't been called by the time they should be, they just go on with their lives, oblivious to what might have been. The ones who did know they were potentials are maybe more likely to be called? They just don't last long, so sometimes it's necessary to bring in one of the untrained girls? I don't know. Just a thought. Or, maybe they do become watchers - passing on all they've been taught including the fighting skills.

I've heard that Angel had a bigger male audience than Buffy did, and I'm sure it was because the primary strong characters were male, whereas in BtVS the males were more sidekicks, boyfriends, etc. Guys just aren't as good at admiring strong women as we are at admiring male heroes. I did, however, think Angel was a pretty well-done and slightly more grown-up show than Buffy was in it's earlier seasons. Whether that's due to the characters being older, or because Joss had learned more about what would appeal to an audience, I don't know.