Well, there are plenty of window managers for X11 and I was under the impression that they only managed window placement and borders. I tried quickly reading about it when I was replying, and found the some window managers (icewm) supported themes only this way (themed borders), while some seemed to support more. However, it's not a window manager thing anymore, it's a widget library which does the theming support. If you want widget library with theming support, you can do it under windows as well. Not a problem. I'm under the impression that you only get the theming to work properly under X windows if all applications you run are using the same widget library (or happen to support same theming mechanism). I'll research this later.
Also, that bb4win is not a PORT, it's a reimplementation and somewhat sucky at that, happened to be the only one I remembered quickly. As additional bonus, I think it handles skinning through external application, for which there are alternatives as well. This isn't an issue of application portability, this is just some kids reimplementing a toy for windows.
About application development, I'm sorry but in real world software is written in a goal oriented fashion, and what goes into actual code doesn't matter. Good code is always great thing, but it doesn't matter how good the code if something important doesn't work. And it doesn't matter how good the code if the damn thing works. For server applications, "small" used to mean "takes less than half the system resources" in some cases, and if your business needs a software that performs some task, you're going to pay even for crap if it's really what you need.
Also, I'm not trying to insult you. You're out of touch of reality if you think that all people would suddenly be bad programmers if there are some bad programmers out there. Obviously the guys with one year of visual basic experience won't be writing compilers and interpreters. Big deal!
Also, regarding to understanding a system, a point you made up early in the post. You seemed to enjoy just punching it in my face, as if we're having an ego fight of some sort here. I pointed out my lack of knowledge on the X11 WM theming details because it sucks to pretend to know something when you don't. I have an idea how I think it goes, but having never worked with the theming crap I don't have any concrete experience. Now you're somehow extrapolating that this means I don't understand linux.
From what I understand of the theming issue here, windows approach is indeed a lot better. The issue with defwindowproc replacement is applications that have been written to expect something of it although the system makes no such guarantees. This includes hacks like adding new buttons to captionbars through evil trickery and other such stuff, even done by big players. Windows XP changed how things render, and apparently had some attempt at theming. I don't know details of how it works, but I recall some applications didn't like it.
I cannot possibly see how a looser approach to doing things is better. The whole idea of pixmapped themes just doesn't fit the X11 design. You can no longer run the applications remotely unless you're ok with them eating shitloads of bandwidth. Advantages of X11 just don't work together with the modern crap.