Not all Danes live for such a "short" time, of course.
True, not all of them live to only be eight years old. However, you will never find a Dane living as long a life as a poodle or a sheltie. My friend had a Dane that live to be almost eleven, and that was very, very, very old for a Dane. Her vet and breeder were amazed. Whereas almost eleven is not old at all for a small dog, which can easily live to be in their late teens or even early twenties with proper care.