It would seem to be a natural progression that if you’re using Google services for 90% of your web usage (Google, Maps, Gmail, Blogger, Sites, Docs, …) then a Google browser would make things run “even smoother.”
This is something that Internet Explorer has had in a way for some time. …and Firefox has 20% without being the default install in any set up (unless some Linux distros opt for Firefox over the native WM browser). 20% of web users made the choice to use Firefox. IE 6’s share is 25%, so I would venture that that 25% did not *choose* IE. In fact, 0.13 percentage points of IE traffic is pre-6.0.
Google will have a much more effective platform through which to push their browser.