I don't understand how so many people are missing the point demonstrated by http://www.focusontheuser.org/. It uses information available from Google search to inject twitter, facebook, etc results into the "your world (as long as it's google+)" module. The ranking it uses is Google's ranking of the relevant results. No special API access. No back-end deals. No money. It's stuff that's available to Google and that Google already has and has already ranked.
If they choose to dilute the worth of their search engine by injecting less-than-relevant (according to their own relevance algorithm) results in order to attempt to grow Plus (presumably hoping that'll ultimately increase the revenue to offset the losses on the search engine side of the business), they are perfectly within their rights to do so. Just don't buy their "oh we'd be happy to show more stuff but boo-hoo we don't have the data" line -- they totally have the data, and it doesn't require sweetheart deals. The only thing they can't do is grab your personal social graph and re-rank according to it. So they use something they know is sub-par (Plus's currently very partial graph) and don't bother dialing in relevance signals against their own best-in-the-world search engine.