Isn't it? A dead man's switch is a device that triggers an automatic action upon your death. Information and instructions given to a lawyer fits that definition.
I don't know how it works in the US but there are definitely countries where after x years of disappearance you are legally declared death. And, yes, some people who are still alive and, say, left the EU for some country in South America, are still alive. Which is not my point. My point is that for inheritance purposes etc. there are countries who'll declared you death if you don't give any sign of life for x years.