User blog comment:Crazy sam10/Infinity Ward explains leaving Modern Warfare series/@comment-71.57.202.60-20130601160113/@comment-3967954-20130606071729

Still incorrect; Portal and Half-Life take place in the same universe whereas Modern Warfare and Black Ops don't.

Also, you can't really compare Ghosts to Opposing Force since nobody knows at this point whether it will actually be in the same universe and MW or whether it'll be a different one. Actually, IW did say it'd take place in a new universe, so...erm...