Even if it's a low-quality cable, 100Mbps reliable is still nothing to dismiss anyway. I wouldn't call them out of date. If cat5 has lasted 20-25 years and is still decent, I bet a homeowner would get the same milage out of laying cat6 or cat6a today.
I agree, phone line is also proof of that. My point is many people don't have landline anymore but everyone has mobile.
The key part is "wherever practical". If you can run cabling throughout a house with reasonable convenience, do it. Most of us can't, but can at least plan the central "hub" of devices so that that as many devices as possible are co-located with the main router and can be wired to it.
I really like the "wherever practical", pragmatic thinking. I guess it makes sense to lay some infrastructure for
router/switch/base stations while still leaving everything else on wireless.