I'm not so sure. Don't forget that IE has larger market share than the rest put together. There's a lot of ways MS could leverage their existing monopolies to bind search in. Maybe context searching from MS Office documents, putting a Bing search box on the Windows 7 taskbar...
If Bing is "good enough", then Google could have a big problem.
Who says it didn't? Maybe Google's marketshare (near monopoly?) would be even more unassailable had it not been for Microsoft's (near) monopoly in the browser space.
If Bing is "good enough", then Google could have a big problem.