The 50 bytes figure represents a compressed response. (We actually write all of our pages compressed to disk before serving them -- nothing is served dynamically. But that's for another post...)

The example below isn't the most scientific, but should give you a rough idea.

  Test index page with different static URLs:
  URLs as 4cdn.org -- 23261 bytes compressed
  URLs as 4chan-cdn.org -- 23311 bytes compressed
  URLs as 4chan.org (control) -- 23278 bytes compressed