Geez, os x is completely riddled with tricks you 'have to know', usually achieved by some obscure key combination. Which UI book did they get this out of ? ...
The don't-clutter-my-screen-with-nine-hundred-thousand-buttons-and-menus book?
Joking aside, most OS X keyboard shortcuts actually follow a very rational scheme (which is mentioned in the Apple HIG, IIRC). If Cmd+X performs an action X, both Cmd+Shift+X and Cmd+Opt+X will perform similar versions of X, so you don't have trouble remembering "special" shortcuts.
Example: Cmd+Q quits an application, Cmd+Shift+Q logs you out and Cmd+Opt+Shift+Q logs you out without confirmation.
Another example: Cmd+Opt+Esc brings up the Force Quit dialog. Cmd+Shift+Opt+Esc force quits the current application without confirmation.
I don't think this is an OS X specific thing. I suspect Windows, KDE and GNOME all follow a similar HIG.
(No, none of those shortcuts are good for your RSI.)
