Comment 23 for bug 706458

>>exactly, it seems as if this, feature was simply excluded as if to
>>separate Ubuntu from the "standard" of commercial OS's

No, it's a matter of bucking a trend for the sake of internal consistency. It's not as if the feature was there, then was removed; it never would have made sense with the grouped items. Clicking the item either launches the application or brings it to the fore (and in the case of multiple windows, allows you to select between them while doing the latter.) There's no reason to create a special case for a lone window that's already focused (and further to make it so that a window alone in its group can be minimized from the Launcher but others can't.)