To see the difference between these two scenarios, ask the following question: "what policy should I precommit to before the whole story unravels?" In Newcomb, you should clearly precommit to one-boxing: it causes Omega to put lots of money in the first box. Here, precommitting to push the button is BAD: it doesn't influence FOOM vs. DOOM, only influences in which scenario Omega hands you the button + whether you get tortured.