Google Plays Poker
2. It's not too late for Google to enter the OS market. Google is a lot like Apple, they don't invent things, they "perfect" things. Google did not invent search or email, but they took those to the next level after the markets were quite mature.
3. Google has amazing experience making OS. They've built very complex data storage systems to be infinitely scalable and triple redundant. Here is a white paper on the file system component of their storage systems: http://labs.google.com/papers/gfs.html . They must have done some Linux development to get the storage systems so mature. And don't forget about Android.
4. Google may be targeting netbooks, but look at the larger picture. It seems their long-term goal is really cloud computing. As you mention, Google will encourage and develop the cloud concept, but I think they have much bigger plans for cloud computing. And Netbooks are just a foot in the door--what better way to sell storing data off the computer than on a cheap and puny computer that holds non-professional data and is not designed to be a long-term computer.
Google has an amazing long-term vision and I have a feeling that Chrome OS is not an end in itself, but a vehicle to take their business models to the next level. Google holds a lot of cards it hasn't revealed.