My guess is that Simpson's marketing strategy is to offer a luxury brush for everyone ranging from the entry level 46, Berkley up to brushes in the multiple hundred's of dollars. Certainly one doesn't need an expensive brush to make a fine lather, but Simpsons is marketing a degree of quality, tradition and luxury which like luxury cars are appeal to more to our emotions.
I suspect that the wide variety of Simpson brushes has to do with appealing to collectors who would over time buy multiple Simpson brushes.
+1