My startup is going thru a series of heavy re-thinks, so I thought I would blog about the different models, and how to approach them in a rather thorough fashion.
On the other hand, a startup that knows what they're doing will know that building out the correct audience is the way to go - if you provide your clients (the advertiser) what they want (quality, relevant audiences, preferably with intent to buy), you can do quite well.
Google isn't a startup anymore. If I were to be asked about more recent startups, I'd list Buzzfeed, the 9gag peoples, Ben Huh's company (can't remember the name) amongst those with quite decent strategies for advertising. You may notice that they're almost all content based companies/startups - that's because it's easier to build audiences with content.