What about contracting a terminal illness like cancer where you might not be able to work. You need a job to keep your healthcare but if an illness or disability that you have or get at some point stops you from working and you need to pay for that healthcare, what do you do?
I feel like Linux is good for power users or users like your grandfather who are not very tech savvy. The issues arise with users savvy enough to get themselves into trouble but not enough to understand how to fix it or how to do a slightly more advanced task.