Over at SAI, the chart of the day suggests that ChromeOS is a jab at Windwows (duh) and that Google needs the OS to succeed because it is the best hope to kill a weaker Microsoft. Despite Microsoft's attempts to break out of the doldrums, and the extreme diversification of their product offerings (many of which never stood a chance of working)- Windows remains the cash cow for the giant.
If I were Google, I wouldn't try to win the war against Windows under current conditions; I would need more things to fall into place.
Android users are wising up to the Google Platform, and applications for Android are proliferating. Windows Phone 7, how are you feeling?
Bing is getting better, has differentiated itself and is integrating with Facebook more obviously (the future of social search is very scary for any company that does not follow Bing's lead)- that's got to be scary for Google.
ChromeOS apps would all be web apps, and the value proposition would have to involve the cloud, and applications that are enhanced by always on-data networks. WiFi in the current sense just will not cut it. You know what would? 3G/4G wireless connectivity built in.
ChromeOS laptops might be a miserable failure like the Nexus one, but if Google sold them at a loss, they'd exact a far more painful loss on Microsoft. With onerous license fees from the essential connectivity, Google has to own the key patents in order to reduce its costs. This illuminates why Google may be fighting so hard against Apple and RIM for Nortel's 3G/4G patents.
When yo sign into Google Apps, use email, docs, spreadsheets, watch Youtube videos in the Chrome browser, and android apps all day, getting served advertising by Doubleclick until you remotely program your Google TV from your android phone and watch The Office when it's convenient for you...that's when Microsoft dies. And with the exception of GoogleTV, I haven't named one thing above that sucks.
To do the same thing on Windows/microsoft/Bing/MSN/Xbox, you're making some compromises along the way, for sure. It's not a done deal, but it's for all the marbles.