The two cats we had in Germany were both outdoors cats and lived 15+ years. One died of cancer, the other got an infection he never quite recovered from. That second cat would beat up German Shepards in the blink of an eye. I've seen dogs give the hedge at the back of the yard a wide berth.

They were both very street-smart, but we did have the occasional visit to the vet because of wounds inflicted through fighting with other cats.
As for the life expectancy of indoors versus outdoors cats, that question has also been asked at
Snopes. I've found one paper through Google Scholar that looked at causes of death and life expectancies. Here's the summary from that article:
Quote:
The authors studied causes of death for 1,044 dogs and cats. The main causes of mortality are natural death (17.90 %, N = 187), poisoning (3.80 %, N = 40), road accidents (5.20 %, N = 54), euthanasia (7.60 %, N = 79), infectious diseases (8.10 %, N = 84), cancer (24.70 %, N = 258) and chronic organ diseases (28.60 %, N = 299). Animals dying a natural death had 15 years’ life expectancy. Poisoning, road accidents and infectious diseases (17 %, N = 178) are associated with a mean life expectancy of 5 years. Euthanasia by cessation of therapy, cancer and chronic organ diseases now constitute most of the mortality causes (57.20 %, N = 597) and are associated with a mean life expectancy of 12 years. Likewise, the survival rates are respectively, 83 % up to 5 years, 75 % up to 8 years, 50 % up to 11 years and 20 % up to 15 years. Thus, campaigns against straying of carnivorous pets and early vaccination programs have contributed to an extensive reduction in early mortality. Concurrently, and as with human beings, geriatric medicine, late-life support and euthanasia constitute new concerns for ethics and preventive medicine.