That's because google doesn't have a chrome OS manufacturing division. However, it is fully dictated by google, is the most high end chrome book, and marketed as google's chrome book.
The nexus in comparison is a cheap device bested by many high end devices.
I understand bmac4 and others like the $300 nexus, what I don't understand is the hostility to a higher priced variant that satisfies others' needs too. It is something iPhone lovers tend to be ridiculed for always, shutting down choice.
So does the stock android S4 suit your needs for an android phone? Looks pretty sick if you ask me.