Your car can "break down" for reasons as simple as blown fuses or low fluids. Having a working knowledge of basic auto mechanics can help you determine whether something is or is not a problem. Furthermore if the problem is simple you can fix it yourself instead of waiting for a tow, getting a taxi home and waiting for the repair shop to open in the morning.
But other things, like cars and drains, matter very little to me. So those are things I pay other people to do. For a car nut, learning about Jade 403 might be a waste of time when you can just buy a new book. But for me, that's pretty valuable.
Sewing is somewhere in the middle, and I've had friends do simple sewing projects for me, and that's been really useful.
I think the real worry isn't about whether someone knows how to replace a hard drive in a MacBook—the real worry is or should be people who seem to have no real skills at all.