Microsoft today struck a search deal with twitter and facebook -
.. Microsoft has reached collaboration agreements with Twitter and Facebook to get their members' public status updates and messages indexed and presented in useful ways on the Bing search engine...
Read more here: http://www.pcworld.com/businesscenter/article/174061/microsoft_strikes_search_deals_with_twitter_facebook.html
And Google posted this on their offical blog
... we are very excited to announce that we have reached an agreement with Twitter to include their updates in our search results....
Seems to me that twitter integrated with both search engines, and not the other way around :) Oh! well, what do I know!