Google vs. Google, Chrome OS vs. Android, Starting on Black Friday (Nov. 26)?

I don’t understand why Google has two tablet platforms: Android and Chrome OS. Android makes sense to me. A mobile OS that can function in both connected (3G or WiFi) or disconnected states. Chrome OS, on the other hand, is a puzzle. It harkens back to Larry Elison’s Network PC concept to a device that only functions as a computer when connected to a network filled with application and server resources. How can this work in a world where 3G data is limited in chunks ranging from 250MB to 5GB per month?