Commenter Myron A. Semack asks via the Suggestion Box why there is a hardware notification icon that doesn't do anything. This is the notification icon that is left behind if you dismiss the hardware notification balloon.
I don't know, but I can figure it out based on information both you and I already know.
First of all, notice that the only way to show a notification balloon is to associate it with a notification icon. After all, the tip of the balloon has to point to something. Therefore, it's not surprising that when the balloon shows up, a notification icon also appears. You can't display "just a balloon"; you have to attach the balloon to a notification icon, and if you don't have a notification icon, you'll just have to create a dummy icon to attach it to.
Second, you already know that taskbar notification icons are not told when the user clicks the × to dismiss the balloon. If you dismiss the balloon with an ×, the dummy notification icon still hangs around because it doesn't know that it's just standing around for no reason.
When you dismiss the balloon, you just leave the dummy icon behind, and the dummy icon is pretty dumb.
You see this dummy icon in other places. For example, if there is a delayed-write failure or if the system needs to grow your pagefile, a balloon appears to let you know about the situation. These balloons are really error messages from the kernel, but repackaged to be less annoying. If you've used earlier versions of Windows NT, you'll remember that these messages used to be in-your-face pop-up message boxes. The kernel folks agreed to add an option (on by default) to auto-convert annoying pop-up message boxes to balloons. But all message boxes can do is show some text and collect a response. They don't have a customizable right-click context menu or a tooltip, so there's nothing to attach to those behaviors when they are auto-converted to a balloon.
I guess clicking on the dummy icon could redisplay the balloon. That would at least make it slightly less dumb.
Update: Commenter John points out that my memory of how balloons are dismissed is incorrect, once again demonstrating that this Web site is for entertainment purposes only.