This page seems out of date or incomplete. LXDE requires a window manager, and currently none is automatically pulled in by the lxde package. The pacman command should probably be: 'pacman -Sy openbox lxde gamin' -- but I haven't tested that to see if it works. Alternatively, a section describing the alternative window managers that can be used with LXDE and how to install them should be added.
(For now, added a note clarifying the fact that some window manager will have to be installed for LXDE to work. Agreed that a more extensive re-write of this page might be better, but I'll leave that for somebody who knows LXDE better than I do.)