In discussing whether hardware vendors should make their own OSs, if the low level is commoditised enough you don't need to replace it with a browser, you just need to pick the one that better suits you (e.g., Apple with FreeBSD).

As far as the user experience goes, non-Windows systems are still handicapped by hardware and software compatibility issues which are decreasing in relevance, especially for a hardware vendor who can ensure that at least the hardware it ships is fully supported in their OS of choice.