Here's the main sticking point in your argument for most people: it is not the Big 10 championship that makes the Michigan/Ohio State game big. Do you care less in years where the Big 10 isn't decided by the game? There are few fans that think of winning the Big 10 first and beating Ohio State second when this game comes around. It is always about beating OSU and the Big 10 championship is just icing on the cake.
At the end of the day the game itself is what matters and all this championship stuff is secondary on that Saturday in November and that is why most of us want it to stay that way. The Game is a self contained event and that's what makes it so special.