It does work, and has for a long time. I can never remember which key to hold down, so I tested within the program right before I posted my response.
You must make sure that only a single side of the effect is highlighted (beginning or end does not matter). Holding the command key down allows for multiple selections to be made. When you click the last effect you want to adjust, keep the mouse button pressed and that will allow you to increase or decrease all selected effects at the same time. If you let up on the mouse and re-click a highlighted effect it will deselect all of the other effects.
If the entire effect is moving left or right, then you have the whole effect selected, not just the ends.