So it does. However I think the real functionality comes from the Command key. Command left-clicking a tab group also displays the list. FWIW I have a Microsoft Wireless Mouse and have the middle button set to be a Command-click when in Safari, I think this enables the operation you described but also allows me to middle click on links and have them open in a new tab, this is how Mozilla and Phoenix/Firebird work under UNIX (which I use at uni).