Firstly, no it isn't. The fact that they need an Internet connection is just one of Chrome OS's many problems.

Secondly, I never claimed Chromebooks don't work offline. I claimed they are nearly useless offline, which they are. They default to storing things in the cloud and using web apps. Getting them to be useful offline requires effort from the user and special effort from the developers of any offline web apps. The fact that users have to keep track of where all their data and programs live is needless complexity which is quite opposed to Chrome OS's supposed focus on ease of use.