User blog comment:Henshin86/Olin unmasks new MP features/@comment-1861566-20101028235038/@comment-1630756-20101029130748

Because of the fact players pay for Xbox Live. Since Microsoft con them out of servers (Which XBL is supposed to pay for) they pay for earlier DLC and more stuff etc. BUT, normally (not always, this was the case with Halo mind and MW2 offline) when players sign in with an extra gamertag, that account ALSO has to be registered with an Xbox Live Gold account, so for most players on Xbox they'll still have to play with Guest accounts.