Cutting Amendola saves $1.6M, and Arrington only saves $865k ($1.6M if his cap hit is spread over 2 years as a post-June 1 cut).
While I agree that neither's performance justifies their cap hit, unfortunately most of that is sunk cost. In Amendola's case, you could save a bit of money by cutting him, but then you'd have to start talking about replacing him. It would take more than $1.6M in new cap money to get a replacement that's at all close to him in ability, and that's without regard for chemistry/experience in the offense.
OTOH, in Arrington there just isn't much money to be saved. I think his real worth is a bit more than the Pats would get back by cutting him. He's definitely not worth $4.6M, but most of that money is sunk cost anyway.
Re: Wilfork, I'm still hoping that he'll just agree to take a 66%-ish paycut, but realistically I don't see that happening so I assume he'll be cut.