I guess to me in the second situation, it is a physician making the decision and he/she is bound by a code of ethics to "do no harm" (Hippocratic oath?). By refusing to operate on the first person, he would be doing that person harm. So I think he is bound by his code to operate even if it means the other six may not be able to be saved. It is not up to him to guess the ifs and maybes of what may happen if he doesn't operate on the first person. He needs to take each decision in the order it comes to him and "do no harm" for that patient.

In the train situation, there is no physician's code of ethics, and the decisionmaker should apply whatever personal code of ethics he lives by, perhaps that being "the ends justify the means" or "the needs of the many outweigh the needs of the one" or "do as little total harm as possible."