Well that depends on Paul Graham's knowledge of other languages. If Paul Graham knows Lisp and only Lisp, perhaps he's falling into the Blub paradox when it comes to Prolog. But if Paul Graham knows Lisp, C, Smalltalk, and Cobol, and has all the necessary language concepts from those to understand Ruby and Perl even if he hasn't used Ruby and Perl extensively, then he's on decent grounds to claim that Lisp is more powerful than those languages.

The blub paradox comes from someone who only knows Pascal doesn't understand why you'd want classes or functional programming. (We're assuming he only knows classical Pascal, not Delphi.) It accounts for the resistance of C hackers to object oriented languages (as illustrated, rather passive-aggressively, in such books as Object Oriented Programming in ANSI C), the resistance of Java coders to first class functions (we have a design pattern for that! it's called "functor"!) and so forth. It doesn't apply to someone who knows Haskell criticizing Java for OO fetishism, or a Java programmer scoffing at Pascal for not having classes.

And the only place where I've ever read pg as critical of another language's abstractions is his remarks on Prolog. Now, that might be because he's fallen into the blub paradox, or maybe he has a good enough understanding of Prolog to authoritatively say it's only useful for 2% of problems and gets in your way the rest of the time. I can't read minds.