Your last sentence is the point: it doesn't matter if there are alternatives which are either unused and so far the only company which has figured out how to out-drive Google is Facebook, hardly more responsive to the rest of the web's needs.

That was the problem: in search, Google effectively has no competition. The fact that there are other areas like social networking doesn't change the fact that if you're a website operator you have to work well with Google even if you can write off everyone else.