People want to believe the world is simple, and that learning one PL is enough. Once you know Java, why learn another one? Either they're all the same, or they're so radically different they must be weak in some critical way.
When you grok Lisp, and realize that it is actually practical, you realize that you've only scratched the surface of the PL problem... and that's scary for a lot of people, especially as there's a tendency to overestimate the barriers between languages. (The Internet runs on components written on all sorts of different languages.)
it's worth mentioning that the dot product would be normally be written as (reduce + (map xs ys))*
Yes, I had that thought, too.
In fact, that formulation is too slow for, say, large-scale ML. I've been getting a lot of mileage out of Prismatic's hiphip library... and I really look forward to, about 5 years from now, when Clojure is as mature for numeric programming and ML as Python is with Numpy, Scipy, Numba et al.