How much of a contingency plan do you need or want to commit to for a backup center? The contingency plan for Tretter is called starting Center Corey Linsley and backup Don Barclay. And before everyone busts open an important artery, while Barclay is limited, you cannot keep a backup on the roster for starter money in a 2nd contract. The numbers won't work. Tretter is also not Mr. Reliable.
Lang simply got more guaranteed money than the other two teams chasing him were comfortable with. Its a near record for guaranteed money. For a guy with an injury history and coming off ankle/foot surgery. He might make it to the end of his contract, but previous history is not on his side.
The contingency plan is for younger guys to step in and get better, just as Lang did when he was a youngster.