This looks at things somewhat in reverse, but I think that there is some logic behind it.
Look at this season's Cleveland Cavaliers. It's basically the same squad as last season. The only difference is now they have no Lebron James.
Last season they won 61 games, this year they are on pace for 12. so basically Lebron James is worth 50 wins by himself... Of course the math doesn't hold up if you add Lebron to a 40 win team for obvious reasons, but you get my point.