I read an Amazon review on the game and the person said the offline mode didn't seem to work for him, the game itself kept giving him an error 'Could not connect to Steam.' Now while I use Steam a lot and absolutely love it, I've never had issues with offline mode working once they ironed it out. I've only gotten that particular error from Steam if Steam is bogged down or my internet is out, and even then I still get the option to start offline mode and play.
Personally, I just think Amazon is full of anti-Steam trolls and people who spread FUD, but I wanted to make sure.