(An example of this sort of mass production is pg's advice to incorporate as a Delaware C corp. Advice like this can save your fledgling startup from a week of legal research. Having 'mass-produced' shortcuts to these sorts of managerial microdecisions can make or break a startup.)
When you can share the same overhead costs over 10 startups and expect 9 of them to fail, that's more palatable than spending the overhead 10 times for each individual company.
And it's not just monetary costs: you can get more done when you have all the companies demo day together, simply by having to arrange fewer meetings individually, and less time travelling/setting up etc.
Sequioa, Accel, Kleiner, and NEA for example have all made a similar amount of (or more) investments in startups than YC. I think it's a bit of a stretch to say that YC is more comfortable than most VC firms. You just don't hear about the other ones' failures because they're less publicized.
YC experimented with pushing it back even earlier in the gestation process, to pre-idea (pre-conception, if you will), and just backing team-quality. But that didn't work out well.
Perhaps not being able to come up with an idea is a crucual indicator of team-quality? A start-up isn't just one idea, but requires thousands of ideas along the way, like a movie. Or maybe passion for a specific idea rallies people round.
The details vary slightly (as the other response said, music studios typically take the rights to the album in exchange for royalties, rather than directly becoming a part-owner of the artist) but the basic model looks very similar to me.
At a push, I'd go with - Investing in stocks:Vanguard :: Investing in companies : Random funds that will only invest if you have a brand-name lead investor