>> This is as opposed to old Gnome 2 and other desktops where you have at least two different places to go (task bar or menu/shortcut) depending on what you want and whether the app is already open.
>People are used to this. It's how most computer UIs work.
Some people are. Many really aren't. My parents usually end up with three or four copies of Thunderbird running after a typical session on their desktop, because they keep launching a new instance rather than clicking on the running instance in the Window list.
Unifying the launching and activation of tasks is one thing that Apple really got right in OS X (though I'm sure they weren't the first to think of doing so, I think it's reasonable to say that they popularised it, now that it has been adopted by Windows 7 and even GNOME 3).