I think you're mistaking the parent poster's argument. Immutability is at its most useful when it's the norm, rather than the exception. For this to work, the core language needs to very strongly encourage immutability, to the point where in-place mutability is considered something only useful for low-level performance tweaks.
It's not that Clojure is new - there are plenty of older languages that have a strong core of immutability. The point is that it needs to be at the core of the language in order to be pervasive.
> You just made that up. Clojure was designed to be able to run on the JVM.
No he didn't. The Clojure rationale page talks about separating languages from platforms, and this subject has come up often in talks and on the mailing list. Clojure has already been ported to Javascript, and there are various projects to implement Clojure in Python, Ruby, C and Lua - that I know of.
There's also a lot of current work going on in abstracting out the Clojure analyser and compiler, both to bootstrap the language, and to make it easier to derive ports.