IE9 hasn't necessarily won the race yet.
Standards evolve at a frantic pace, with a lot of the spec being written in retrospect to accommodate progressive browser implementations. While the Webkit and Gecko teams work iteratively in an environment of rapid development, IE versioning has always come in disparate version releases which do not upgrade gracefully rather than feature-laden optimisations in the form of point-releases. If IE9 wants to stay ahead of the game, Microsoft would need to fundamentally change the way the IE team works — but the cost & security issues of core MS product uptake make such a model difficult to implement.
In the meantime, check out IE9's CSS3 support — abysmal!