Why Google Doesn't Want MS To Own Yahoo
"The Internet has evolved from open standards, having a diversity of companies," Brin told The Associated Press after the event. "And when you start to have companies that control the operating system, control the browsers, they really tie up the top Web sites, and can be used to manipulate stuff in various ways. I think that's unnerving."
Microsoft has a lot riding on their various software products, especially Office. Google seems to be of the mind that such products will mostly be web-delivered one day and that eventually OSes won't be much more than a preference as a result. The idea of letting Microsoft potentially lock early web-based products into a given OS might kill the whole concept before it really takes off, and that's not something that Google really wants to see.