You're correct. I even have a spam-only email account for such purposes. When I signed on here I understood that submitting some personal information was part of the "price" I pay for the service. If it was only necessary to do a one-time log in to Steam in order to register the game I might be okay with that. However, my understanding (And Greg can correct me if I'm wrong) is that you must have Steam's app installed and therefor running in the background in order to even play the game in single player mode. That is unacceptable. Although Steam's EULA and it's intentions may be exemplary at present they're one buyout away from being something else.
Only info you need to provide when creating new Steam account is valid email adress. It was already confirmed that you will be able to play Civ5 offline (via Steam offline mode) so I dont see amy problem.