I would imagine that, as with cars, a well cared for and maintained camera will tend to last longer than the Nikon quoted average, while one that sees more active duty (lots of days in the cold and heat, outdoors in dusty environments and weather) may tend to give up the ghost sooner. And as was said, if the camera is otherwise in good working order, $300 isn't a lot to spend to keep it going if you loved it enough to wear it out. The average user will likely be ready to move on to new technology by the time it does, so they get a choice - repair or upgrade.