Google has already proven their willingness to degrade their search experience for non-Chrome browsers, by splashing a Chrome banner ad on the Google search home page[1].
This is about capturing more marketshare for Chrome, pure and simple. Eventually "old browsers" will be replaced by "browsers we don't care to support" will be replaced by "browsers that aren't Chrome." In the end, there's a possibility that Google's client software will be required to access Google's services.
Do you think that's farfetched? That Google is committed to browser diversity on the web? Then look at their vision for the desktop: Chromebooks, which do not support installing any web browser that's not Chrome.
[1]: http://techcrunch.com/2012/09/04/firefox-install-google-chro... and http://timothycope.com/wp-content/uploads/2014/05/0529201400...