You're assuming that Google's algorithm treats a small restaurant website and a site like Seamless equally based on the same SEO ranking factors. That assumption ignores some important factors;
- Seamless have enough capital to buy the ad space at the top of every restaurant search. They'll always be at the top.
- Google weights things like inbound links highly. A massive site like Seamless will always win on those factors.
- Google allegedly considers domain and website age as important in pagerank. Seamless has an advantage over new restaurants there.
- Most importantly though, for all we know Google's algorithm could simply be biased in favor of Seamless. It's a black box. There could be a rule that just says "if (seamless.com) rank += 10000". If Google users prefer SERPs where that gets applied then it'll be there. There's no reason to believe pagerank is fair.
- Seamless have enough capital to buy the ad space at the top of every restaurant search. They'll always be at the top.
- Google weights things like inbound links highly. A massive site like Seamless will always win on those factors.
- Google allegedly considers domain and website age as important in pagerank. Seamless has an advantage over new restaurants there.
- Most importantly though, for all we know Google's algorithm could simply be biased in favor of Seamless. It's a black box. There could be a rule that just says "if (seamless.com) rank += 10000". If Google users prefer SERPs where that gets applied then it'll be there. There's no reason to believe pagerank is fair.