In theory, and practice, you can build a site in anything with enough effort. Scheme, Scala, Go, Haskell, Clojure, etc. However, it's good to know that other big sites are using your preferred choice. A lot of usage usually indicates mature frameworks, larger user community, ability to Google common issues, find developers as you grow, etc.
What was that YC site that initially used Lisp but switched to Python at the end because they couldn't get something to work?