This does not include Clojure, nor Leningen (the Clojure build tool), nor does it work on Windows or any environment that does not have apt-get. No doubt, you will end up with a perfectly suitable environment for playing around with SBCL.
edit to add: How does one even know to install SBCL and hit M-x and type slime to get started? You and I might already know these things, but it doesn't really help a stone-cold newbie, they still need a more concrete starting point.
How does one even know there is such a thing as SLIME or Clojure or Leningen? How does one even know that there are computers or that they can be programmed? How do you know?
I do not understand your point. If someone wants to learn Clojure, she certainly knows about Clojure. But she may not know (or care) about Leiningen, Emacs and the rest.
His point is that he doesn't know you need SBCL to program SBCL. At this point, the problem is not that it's too hard to install, it's that he's too dumb.
edit to add: How does one even know to install SBCL and hit M-x and type slime to get started? You and I might already know these things, but it doesn't really help a stone-cold newbie, they still need a more concrete starting point.