Many people have been criticizing that each new Porsche looks like the model before. And they are right. But Porsche learned the hard way that it doesn't always pay off to be brave in designing cars. When they launched the Porsche 928 it was very different to anything they had done before. It had an 8 cylinder engine in the front, four seats, was wide and big and it really looked very different to even any other car on the road, maybe with the exception of the AMC Pacer. And you don't want to see this as a design icon. Well the car also suffered from some weaknesses including being very thirsty and having the aerodynamics of a Volkswagen Beetle. But most of these things got sorted out over time and the car actually became quite good. But not good enough to no being successful enough. And never since Porsche announced any radical car like the 928 any more.
Other examples needed? Look at the Bangle effect at BMW. Or look at the TVR Tasmin (called the Wedge). Or what about Pininfarina? Most if not all of his cars were more evolutions than revolutions and he know quite well why he worked like this. Beauty has to be accepted by the buyers and you can't stretch it too far.