Considering that a 450W PSU is enough for just about any reasonable PC, whether low-power computers are a thing of the past or whether they aren't is a moot point.

Remember that PSUs are terribly inefficient below 20% load, meaning that a 650W PSU is a terrible match for a computer drawing 90W when idle, because it will be at 14% load. And modern computers have various power-saving features and draw very little power when idle.