3 Racing improves the breed
The 911 never got an engine as powerful as the top guns from Ferrari and Lamborghini, but it usually outperformed them in real world. In the illegal supercar street racing I saw (as already mentioned in the page for 911 RS 2.7), the first two leaders were both 911 Turbo 3.3, followed by a RS 2.7, a Carrera 3.2 and various other 911s and 944s. The first 4 were leading a Lamborghini Countach QV and a couple of Ferrari Testarossa, then an older 308GTB and lastly, a Mazda 323 turbo 4WD. This was not an individual incident. In fact, the 911 turbo of various versions won all but one Macau Supercar Cups in the past decade. The only car ever beat it was a F50 driven by a professional racing driver.
What made the 911 so outstanding in real world was the experience gained from motor racing. As we have learned earlier, from the very beginning Ferry Porsche decided the car must be suitable for racing, therefore adopted dry-sump lubrication and rear-engined instead of front-engined (although mid-engined was ruled out in favour of practicality). In the following years, the 911 adopted many technologies learned from and thoroughly tested in motor racing. For example, the Nikasil cylinder was transferred from the 917 endurance racer, so was the entire brakes for the first Turbo 3.3. Likewise, the turbocharging was first explored in the 917, but Porsche further tested it in the 911 Carrera RSR turbo before applying to the road-going Turbo. Without a racing program building around the 911, "racing improves the breed" could hardly be realised.
The value of racing program was that it provided an opportunity for proving new technology meeting the requirements for reliability and durability even under the highest stress. Therefore you can hardly hear a 911 engine (including Turbo) overheat. The same couldn’t be said for Ferrari and Lamborghini. Racing experience also concentrated engineer’s vision to reduce lap time rather than playing with horsepower game. As a result, the 911 always got powerful brakes that helped out-braking others into corners. In contrast, the Italian and British didn’t paid much attention to braking until recently.
Lastly, if not benefited from racing experience, the 911 wouldn’t have lasted so long. The continuous enlargement of the flat-six engine would not have been possible without thoroughly tested in racing models. To withstand the stress under racing, they learned what should be strengthened and what could be lightened, eventually enable the bore to be stretched to 102 mm without deteriorating reliability.
4 Continuous development and derivatives
Without long-term commitment to development, the 911 would have died long ago. Although the basic rear-engined layout was never touched, it received engine enhancement every few years. Then diversified into Carrera, Turbo (plus the rarer RS). Also came various body styles to choose from - Targo, Cabriolet, Speedster, Turbo-Look - and then added with optional 4-wheel-drive and Tiptronic. Besides, there were many "special" editions launched in regular interval, such as Club Sport, Turbo S etc.
Major updates like the 964 and 993 injected new lease of life for the last 10 years, including new engine, suspensions and transmission. Eventually, the 911 shared virtually nothing with its origin, except the basic layout and philosophy defined by Ferry Porsche. No other cars ever changed so much.