Agreed, the assertion that doctors and nurses aren't responsible for people's lives on a large scale sounded bizarre to me, and I also agree comparing totally different jobs is meaningless. The reason it is done is because the fallacy of relative privation is one of people's favourite logical fallacies, to be applied whenever anyone complains about anything. legitimate or not, in order to provide an excuse as to why nothing should change. It effectively asserts everyone should be grateful for their lot as long as there exists someone else in a worse condition. By such logic, the only person who has a legitimate reason for complaint is the one who has it worst in every possible way.
Fallacy of relative privation: Trying to make a scenario appear better or worse by comparing it to the best or worst case scenario.