I do think we should be worried about letting google get too strong a walled garden. The most worrisome thing about google is that we depend upon so many google products, that it might be difficult to see what we are missing if they started to overly favor google offerings. I don't think google has gone there yet, but it is something to keep track of. That being said, twitter has no excuse to complain if they did simply remove themselves from google's results. I suspect that in fact they negotiated and got a better deal going exclusive with bing.