My wife has always said she wants to go before me. I think it's a bit selfish, but also kind of sweet that she doesn't want to live without me. I've noticed that sometimes people go back to work after they retire because they need the money, but then there are those who just want to be busy. They don't need the money, but they just want to feel like they are contributing and many times they are willing to do those jobs that other people wouldn't want to do, so maybe one day if we can break out of the pay check to pay check cycle, we might see more people focusing on beautification of our communities and things like that.
Or she wants you to suffer after :D
That sense of "contributing" gives a sense of worth. I imagine that person who can't work for a long period because of illness and has to rely on family to support, must feel pretty crappy.
My friend is actually in that position right now and yes it wears on him a lot. They don't need his income, but he still likes to feel as though he is offering something.