I think it's normal to quit an application when that application is active. If you have to launch a Finder script/command to quit an other application than the Finder itself, then it just doesn't feel natural.
Imagine the quit-widget sitting at the left-top corner, when you click it all the Widgets that are open will fade away (or some other smooth animation, but not the zoom-effect, because that is been used for hiding dashboard) and then Dashboard will quit. To launch Dashboard again, you simply press the icon in the Dock.