Actually, ChromeOS isn't just for netbooks. It's for a world where everything you want to do on your computer is available via a web service. Netbooks happen to be suitable for ChromeOS now because the web services available today generally don't require much heavy lifting client-side. Especially if NaCl/PNaCl takes off (who knows?) that very well may change soon.
That's why ChromeOS as designed is, in my opinion, actually unlikely to become defunct anytime soon: I personally suspect the percentage of consumers for which ChromeOS's capabilities are sufficient will continue to rise over the next few years.