Google want to have Google search engine built on windowsphone not just bing on search button options.. That's why Google do not release there official YouTube application for windowsphone.
Assuming the OP had the reading skills above that of a 10-year old, I still wouldn't believe him. I never heard Google make a peep about Apple using Bing for siri.
Google has a search engine app in the market. As for the YouTube app, they've already released it but they eventually took it down because MS didn't get the requirements being asked by Google (not sure what those are but that's the reason).