My argument wasn't that knowing someone's intent is necessary. It's just that it focuses the advertising much better and as such demands far higher CPMs. Facebook can guess all they want, and if they do a perfect job (far better than technology allows currently) they'll guess as accurately as Google does now.
I agree with your main point, but the bottom line is that even if Facebook's CPMs are lower than Google, it doesn't mean that Facebook can't make a ton of money from advertising or that advertisers can't get good ROI on Facebook. You don't need to be Google to be a successful advertising platform. Also, don't forget that Facebook is still young and I'm sure many advertisers haven't yet adopted it. I have a friend who does internet marketing and he says that, at least in his niche, Facebook CPMs have been increasing by 10% a week.
http://andrewchen.typepad.com/andrew_chens_blog/2007/09/why-...
It's true that a lot of LBS advertising models don't center around intent, but advertisers will still pay a premium for the additional context and relevance of reaching people near the potential point-of-sale. And what about LBS that employ Mobile Search?...
Search implies intent. Better than anything else.
All of the LBS (Location Based Services) haven't figured this out yet, but Location does NOT imply intent. Walking past a pizza store does not mean I'm hungry for pizza.
The question for Facebook is whether any data that they possess does a reasonable job of implying intent. It doesn't have to do as well as search, but it has to do well enough.
The question boils down to "what do you do on facebook that implies intent". The status may be one of the only things.