Other than assuming the worst, there's no reason to assume the game cannot function in single player without being connected to battle.net.
After all (and ignoring that GFWL is crap for a second), I could make the same statements about Fallout 3, Dawn of War, or Resident Evil 5 and GFWL. Being able to be "always connected" for "enhanced functionality". None of them require you to log into GFWL to function in single player though. Or any Steam game for that matter (you can go to offline mode, but then you lose the "enhanced functionality" of steam achievements and friends.
I'd expect something similar to the Steam overlay for the new battle.net.
incorrect. as stated in a sibling post, "open source" is a term such as "flying car." Similar to how a flying car can be called such so long as it flies, open source software can be called such so long as the source is open.
Under the strictest semantics, all that is required is that the source code can be viewed. Everything extra is FUD and propaganda.
In every non-trivial program there is at least one bug.