There is clearly more to this than meets the eye. Saying a 34th pick for Vrabel and Cassell is a steal, is a fantasy football mentality. Tough choices have to be made with the cap, and Belichick obviously has some ideas with what to do with the room and flexibility now created.
Without this part of the deal, even Belichick would agree with any of you that talent for talent on paper, Vrabel and Cassell is more combined talent than a 2nd rounder. But NFL trades aren't just talent for talent. Cassell and Vrabel are only worth more together, if another team besides the Chiefs is offering more, there is no set market value based on player talent rankings when it comes to doing a deal.