This might be true for standard consumer applications that can fit within the web paradigm. However, you then fail to be able to leverage vendor specific interaction paradigms, which is something I want to be able to do, such as the Mac touch strip, the Windows Surface Dial and Pen, or the Gnome title bar/notifications/messaging interface. I like to interact with voice services, so you need something for this as well, or handling the various HiDPI features of each system.