Who's talking about an "AdSense business"? I'm talking about a media business with multiple revenue streams (of which AdSense is just one interchangeable element, and not the biggest element at that).
But that's a topic for another thread in a different forum. The question here is whether PPC makes more business sense than relying on organic traffic. The answer may be "yes" for an e-commerce site or a pure affiliate site; it's likely to be "no" for an editorial or reference site, partly because of ROI and partly because "content sites" provide the raw material for the SERPs that attract users to search engines.