OS' are more resistant to changes because of the effort involved in re-training. In purely consumer space, we already have iOS and android which do offer a more modern approach to human-computer interaction than desktop OS'. The world is simply not ready for anything disruptive in this space. Take WinFS for example.. too early for adoption.

One step in the right direction is ChromeOS (and firefox OS to some degree), and its model IS going to be the future, but the problem with ChromeOS are: (a) web technologies are not mature yet, (b) any new OS should have support for both native and web apps.