I don't understand why Chrome OS is considered to be something revolutionary.
No, Chrome on Linux does not include all features of Chrome OS. (At least, IIRC, based on Google Chrome release blog posts with Chrome-OS-only features identified.)
Hmm. I'm not aware of any unique features in a chromebook. I use a chromebook pixel as my all-day dev machine and I use chromixium (linux with fake chrome desktop) on my two older machines. I've been able to do whatever I wanted on all three.
From your average user's perspective, it also generally looks nicer than lxde and other lightweight DEs (though that's entirely subjective).
For technical users, there's probably not a good reason not to just use a lightweight linux distro, but technical users aren't really their target audience.