Let me list the ways that Chrome starts to encroach on the OS territory.
1. It has a fast Javascript VM, that converts Javascript into native code, cutting through lots of layers.
2. Each Javascript app (i.e a tab) runs in its own process, which the browser manages. So effectively Chrome is the OS layer as far as your JS apps is concerned.
3. The browser provides a nice control panel for managing those tasks and provides stats about its usage - again tradtionally what you wanted from an OS.
4. Chrome is not yet cross-platform, but we can expect it to be cross platform in due course. It is open source with a BSD license, so I am guessing lots of people have already started compiling it to every platform on earth. Expect unofficial distros soon.
5. Layering Chrome on top of a very stripped down Linux or BSD kernel, letting Chrome do all the GUI work is possible. Chrome does not need MFC, it is layered directly on top of a lower level graphics library (Win32). The calls Chrome needs could be done on top of BSD fairly easily. In fact, that is how Chrome (or Firefox for that matter) is really cross-platform - they come with their own widget sets (i.e MFC equivalent) rather than relying on the specific platform's widget set. Incidentally, Java does the exact same thing.
6. OEMs could come up with a 20-30 MB distribution of Chrome, with everything included (kernel, libraries, JS, Flash etc) and bundle it as a web top.
So, yes, Chrome is an alternative to traditional operating systems. The fact that it would include a stripped down BSD kernel doesn't count: from the application perspective Chrome is the OS.
Snark is all fine and dandy, but occasionally exercising the brain cells a little bit keeps them in good working order.