I think he's missing the point by focusing on the GUI -- it's a uniform userland, not a uniform appearance, that facilitates interoperability. User management, permissions and a model for resources go a long way toward making a platform.

As Firefox, Silverlight & al. become more and more like desktops, virtualization allows Linux to become more like a cross-platform application environment. Web apps often find themselves recreating userland fundamentals. The people at Vita Nuova caught on to this a few years ago, and released a version of Inferno (Unix relative) as a browser plugin.