Usually people talk about Lisp's superior expressiveness. The ability to "draw down" (or up) a language to the concepts you're working with directly is a powerful thing, and very few languages do that as well as lisp.

Maybe that's what he meant? "Functionality" of a language is kind of a vague term.

My apologies, "functionality" isn't a very precise word in this case. I meant it in terms of what functionality is in the language's syntax. For instance, Lisp has macros whilst PHP does not. And whilst later versions of PHP do support things like first class functions, they do so in an unwieldy and verbose fashion that negates a lot of their advantages:

    #(* n %)

    (* n _)

    (* n)

    function($x) use ($n) { return $n * $x; }

One of these things is not like the others :)