They also make it up in volume - most owners are hard-pressed to fly more than 100 hours a year (time, money, etc.). Whereas a rental plane can get 200 hours a year pretty easy.
Think about an owner who flies for two hours on a weekend. That's a little over a hundred hours a year - a lot of flying. But a rental plane my fly for 4-6 hours on a Saturday, an equal amount on Sunday, and still be available during the week.
