The Real Reason Why the Prisoner's Dilemma is Not a Newcomb Problem

It is commonly thought, in line with the position defended in an influential paper by David Lewis, that the decision problems faced in the prisoner's dilemma and the Newcomb situation are essentially the same problem. Jos, Luis BermA(0)dez has recently attacked the case Lewis makes for this claim. While I think the claim is false, I contend that BermA(0)dez's reason for rejecting Lewis's argument is inadequate, and then outline what I take to be a better reason for doing so.