What people use on mousepads and t-shirts is up to their imagination. Compare it like Linux. Tux is stable for more than a decade, however, because of this, people can use their imagination, and if you look at for example the LWN penguin gallery you see the strangest of Tuxes.

It was decided from the start of the FPC web site that we did need something to symbolize speed. A running cheetah fits this. A static one much less.

Lastly, because we can do Shrek-style animations today it does not mean every animated film has to be done in such a way. It is the same with a logo: It is not because we can do 3D rendered cheetahs that we should get rid of hand drawn graphics.

Of course, as said, the largest reason why we keep the cheetah is because it is too difficult to draw a new one.