That's a really weak argument. Java is used orders of magnitude more in enterprise, and you don't see anyone proclaiming that as the pinnacle of language design.
And didn't they at one time have to reset the server every few weeks because HN would use up all the RAM or something? That's not something other forums built in lesser languages have to do.
I mean, it obviously works, but would anyone say it works particularly well, even as a Lisp implementation of a web forum?
Also, as a side note, one would be quite surprised how frequently will known companies solve memory problems by restarting processes frequently.
I don't know how Arc does it but Clojure's resources are no different than any of the millions of Java web servers running; just a much better language to run on vs Java for that platform.
But much larger companies are using it also, nearly exclusively.
As far as macros go, the most popular Clojure library for routing web requests on a server is Compojure, and it wraps a lot of low-level stuff up in a tight lisp macro set that makes it trivial to functionally compose your http requests. It's pretty nifty and is used extensively in industry.
Also this web site you are interacting with right this moment as you read this is built on lisp.