[darinwc]

and there's not always a correlation to quality (just what's either a well-known "classic" or a current fad).

People will often spend twice the money or more on lenses that are negligibly better than others. A good example of this is 50mm lenses, where f2 and f1.8 lenses often go for peanuts compared to their f1.4 versions. And the slower lenses generally are just as sharp and have better contrast.