One big flaw in your logic BMU is the risk that Branch assumes. If he returns to only play the last 6 games, he loses tons of income. He is a 2nd round pick, so it isn't like he has pocketed multi-millions. Even if he does that, the Pats still have the franchise tag over him.
However, that strategy not only costs him tons of money, but also comes with the risk he could lose everything if he is injured. If he comes to play the last 6 games and suffers an ACL, do you think he is going to get $6M per season in FA? That is a huge risk to take on, especially given Deion not being the biggest guy in the world. He has been hurt before.