While I agree with the general thought that Belichick can thrown out poor information, he is also candid with certain things when he wants to be, especially if he doesn't believe that there's any reason to beat around the bush.
In this particular situation, our past pattern has shown that we aren't going to dump (or trade, particularly due to the likely market that Mallett would currently command) our veteran backup until our "new" rookie has had some time to digest the large, encyclopedia like playbook, along with many other variables that go along with attempting to acclimate one's self into our team/lockerroom, film study, practice habits, etc. Typically this takes a full year, however there was one time in 2009 when prior year's 3rd round pick Kevin O'Connell looked so pathetic that Belichick was comfortable enough rolling the dice with new rookie Brian Hoyer. Obviously, that is not the norm in these situations.
It's quite possible that Bill Belichick either feels that he wants to have Mallett here on his cheap, rookie deal in the meantime until JG is ready next year, and/or he's well aware of the current market value for Ryan Mallett and feels that it simply isn't worth it. In that sense, there's absolutely no competitive advantage to be gained.