Actually, it can work on the same principle as PPC, except the $/click takes time to work out (you have to send traffic to the site to determine how much revenue it gets you). Analagous to your example is Amazon biding $0.00001 per click - they would simply be outbid by sites willing to pay more for the keywords. The only difference is that with PPC there's a minimum - I think it's 5 cents, though it might have increased to 10 - but you can define an action as an extremely infrequent event. But that difference only comes into play when you've got no competition, and if you've got no competition for a keyword, it's extremely unlikely that it's going to be a lucrative one.
The key point is that Google figures out how much it makes by sending people to a site, and ranks the sites based on that metric. So just like Adwords, there's no getting around the fact that paying Google more (by bidding higher, or on more frequent events) will get you better placement, and therefore more traffic.
The key point is that Google figures out how much it makes by sending people to a site, and ranks the sites based on that metric. So just like Adwords, there's no getting around the fact that paying Google more (by bidding higher, or on more frequent events) will get you better placement, and therefore more traffic.