Umm it sounds to me like you don't realise how big piracy is. People have been playing cracked versions of many popular game titles such as cod for ages through the use of private servers. I don't know the exact details but ive heard about it from friends who play cod. It's the sad truth really.

They have a lot to learn from Valve here, you don't have to enter any serial to play online on their games, and you still don't see people pirate Team Fortress 2, or Left 4 Dead for example.
You don't even have to sign into some account before you get to the menu of the game either.

If your referring to the single player you only have to hit skip, if its the multiplayer your talking about having to log onto your account first then most all recent Multiplayer games require you to do that...nothing new here.