Yes but that requires a click-and-hold, causing the whole dock to resize for the pop-up menu, which is quite slow on my 32-bit MBP maxed out at 2GB RAM. I find it quicker to just click the Preview icon (causing a new window to open as the focus switches), and command+q.

You might want to try command-tabbing and quitting.

Basically with command held down the entire time, hit tab until Preview is framed, and instead of releasing command (which would pull Preview to the foreground), hit Q, which will send Preview the command-q event and cause it to quit.