If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Eliezer's answer (I can't find it at the moment) is that there are many more lives around, and it seems unlikely that U(875,431 people die) - U(875,430 people die) is that different from U(875,430 people die) - U(875,429 people die).
(OTOH, once you've spent $200 to save a life, you have $200 less, and so the marginal utility of another $200 is larger.)