I hear you. I personally don't know how any company would advertise your CG at the same time as your Next gen. Graphics alone the difference is so great and the CG has your biggest install base and probably where you will sell the most units.
So I think it's a case of wanting each game to have it's own time in the Sun. More than let's dupe people into buying both. The people who will buy both like me are going to do that anyway.
History says that 2k has never pulled a madden 06. Even madden NG has said they are not pulling a madden 06 LOL so I doubt 2k in the face of competition would think that is sound strategy. But you never know. So I guess we will have to wait and see.