Web hosting can be a lot more time constraining. As a hosting company you are usually obligated to provide service and support 24/7 to compete. If a company's site is down, they want it back up NOW, not Monday morning. I'm a hosting reseller, but only provide it for companies, friends, and organizations that understand and won't expect immediate support.
With domains, I can go on vacation without too much worry I'm losing customers. If I only checked email twice a week, I would probably not lose an offer. With public hosting, you really need a staff to handle things all the time.