What I mean by this is that San Francisco wasn't the "alpha" city for any particular career path. If you wanted to pursue law, finance, publishing, entertainment, and so forth, the alpha cities were New York, Los Angeles, and maybe Chicago. Even tech was mainly a south bay thing, and it was smaller.
That's not to say you couldn't pursue a fine career in these fields SF, and SF probably was one of the better 2nd tier cities from a career perspective (the only other one I can think of is Boston, similar in that it has top tier universities that do bring top academics to town), but it wasn't until tech hit that SF became a place you would live for your career, even though otherwise you didn't like it here.
This has changed things a lot. People have always come to SF looking for something new, but in the past, really as recently as maybe the late 90s (just before the first dot com boom), people really only came to SF because they wished to some extent to live in SF. I also think this may be what is behind many of the recent "10 things I hate about SF" posts, often comparing it unfavorably to New York or other "alpha-career" cities. In the past, whoever wrote these would simply be living in New York or another alpha city.
It has been a very deep cultural change for SF to suddenly find itself an "alpha" city for careers in a a substantial segment of the economy - in other words, people who moved to SF specifically for career advancement, but would otherwise prefer to be living somewhere else.
I don't see this trend reversing any time soon though so instead of lamenting this change I'll just live somewhere else if I decide to live in the States again.