Historical note: Viaweb was written in lisp, so most of the users had a hard time customizing it (I heard of one book on modifying Viaweb, but have never actually seen it.)
Yahoo eventually re-wrote it in another language.
Whereas if they wrote it in C++, the average store owner Joe would have a walk in the park with it?
Depending on how heavily metaprogramming is relied on, relatively so