Most people don't want or can't afford to have their
  computer running 24/7

I guess I shouldn't make too many assumptions. I'm sure plenty of people are still using Windows on 10-year-old towers attached to CRTs. But my Macbook Air goes several months without a reboot, as did my previous one, and the one before it, going back at least 10 years. I don't even think about it. My servers are rebooted much more often, simply because of kernel patches and upgrades. Fortunately startup is usually quick for both OpenBSD and Linux as, ironically, there are far fewer services and the hardware is less complex than typical consumer machines.