Hold the mouse button down over the icon of an unresponsive app in the dock and get this menu:
Right-click on the icon and get this one:
Same three options. One is vertical, the other horizontal. Clearly they serve the same purpose, but are arranged differently, and in the case of the horizontal menu, poorly. Why are there two menus? Moreover, why does right-clicking on dock icon not reveal the app’s open windows via Exposé the way click-holding does?