That's a very good question, since the page shows five screenshots and one photo of a multi monitor setup for me. In addition, there's a link to https://wiki.haskell.org/Xmonad/Screenshots

I think the screenshots disappear (instead of just going into a single column mode) on very small screens, so people looking at xmonad.org from a mobile phone may not see them. Hm, we might want to fix that, perhaps.