I think the reason to teach something like changing a doorknob isn't really because they're going to need that specific skill. I'd consider teaching it because it's an easy demonstration that taking things apart to fix or change them isn't necessarily a scary thing to do. I bet a lot of people with some minor problem to fix in their home wouldn't be able to do it, not because they can't use a screwdriver but because their instinct is that they are supposed to get an expert to do it.