The browser has become the main interaction that people have with their computers and that's why it's design and competition in the browser market has become so important. Interfaces such as Vista's Aero have largely become irrelevant. Sure there's got to be an operating system underneath but, if you put the browser as the human interface then what's underneath becomes less important.
The growth of the sub-notebook market suggests that often a system that will run a browser and not much else is all that is required.

