Does anyone know why languages like Arc, SmallTalk, Clojure, Scala etc need web frameworks? Is it that there's something special these frameworks/languages do that other languages/frameworks for the web don't do?

I was always under the impression that these languages were made for a specific purpose other than web and hence not used much on the web.

P.S: I read that Twitter's msg queue is in Scala since its faster.

"I was always under the impression that these languages were made for a specific purpose other than web"

Actually, if Arc was made for any "specific purpose" it was exactly the web. Paul Graham has long written about the suitability of Lisp for web programming, and the web site you're reading was the very first real-world Arc application.

More generally, the languages you name are all excellent for trying new framework ideas because of their ability to easily create expressive APIs.