Yeah.. it really doesn't. The DoJ would be all over their ass if there was really a case to be made there.
> Therefore it's a rule for the internet.
That doesn't even logically follow if we assume the first. It is more than possible to use the internet without giving a shit about google's product. Even if it were a monopoly this would be true.
Google changing how their product reacts to RapGenius does not effect anything other than how their product reacts to RapGenius. Just because RapGenius cares a lot about how Googles product reacts to their own does not mean that the rules of Googles product are rules "of the internet".
If Google had the power to set "rules of the internet", then the MPAA/RIAA would have won their battle when Google changed how their product handles search results for torrents. Of course they did not, because Google cannot.
This just shows that you don't understand what a monopoly is. Monopolies are not in themselves illegal, so there is no reason for the DoJ to get involved unless they break one of the laws regarding what monopolies can and can't do.
And, of course they are being investigated for doing exactly that in Europe.