Note that 10.7.x Stickies are still capable of a form of window-shading. That says something to me.
I disagree with your use of the term "belly aching", which implies that the complaints are not justified. On the contrary, I think there's a really need for windowshading, or some functional equivalent for cases in which users have a need to have large numbers of windows open and organized on the desktop, each of them identifiable and immediately available. (That's the best meta-description/justification for windowshading that I can produce at this instant. Please, anyone, feel free to improve it.)
For what it is worth, maybe Apple actually does surveys and has determined people with such needs are actually in the minority. Maybe most people only work with very small numbers of files at a time. If so, I can understand why this function or a replacement has fallen off the high-priority list.
Reflecting... It makes some sense to strictly limit the number of representations (incarnations?) of each document. The document icon is one, the opened document --if it is currently opened-- is another. A windowshaded representation of the opened document kind-of, sort-of looks like a third. From this point of view, the designers allow windowshading of sticky notes because, otherwise, each of these appear in only one representation.
I can't locate it at the moment, but I've seen information that Apple is slowly shifting its model to one in which users don't need to worry so much about opening and closing documents, or the distinction between documents and applications. We'll have to see what develops. I'm hopeful that the designers will at least partly accomodate our needs in the process.
If Herrbutzie's information just above is correct, we won't see a third-party implementation, ever (again). What's to do in the meantime? Look for workarounds, I guess. To me, Mission Control Workspaces/Desktops needs some improvement, but can help a lot. But I still find myself shoving some windows off to the side of my monitor. Shrinking windows to the dock ... to me has very limited appeal.