I don't buy the decision-theory thing. I don't think I can make a quantum coinflip come out a different way by redefining my utility function.

The Oxford Everettians don't think so either. I mean, come on, Deutsch and Wallace are pretty smart people. Let's give them a little bit of credit. If your construal of their view is just blatantly absurd, the problem is probably with your construal, not their view. I tried to give some sense of Wallace's position in these comments.

The point of Wallace's argument is that no matter what your preference ordering over rewards (assuming they obey certain intuitive constraints), you will recover the Born probabilities.