The Rangers and Angels "figured it out" because they are getting more money than the U.S. Mint because of their new regional TV deals. That's how they signed every free agent out there worth a damn.
The Sox deal with Comcast doesn't expire until 2016 and they'll get nowhere near the money, not even close.
I understand your overall point and I agree they can do better but TV money has become the driving factor in a lot of this and the Sox and not well positioned. (Through no fault of their own...)