Now, I know that both Gnome and KDE have what you could call a high level of integration between Compiz and Kwin (Or whatever it's called now) and Metacity, and both can have Compiz replace Kwin/Metacity with Emerald.

However, given that I've never got on well with KDE (And for reasons of avoiding a flame war, I won't go into why for now) and Gnome has started to get a somewhat clunky feel to me, I'm starting to look elsewhere. The problem is, the moment I look elsewhere, it seems like Compiz isn't interested any more.

For example, one of the possibile alternatives to a full Gnome/KDE session I often use is an Openbox session. Why can I not have Compiz work with that, and keep the Openbox WM style, like Compiz without Emerald uses the Metacity style?

Of course, there are other WMs I'm thinking of trying, such as LXDE and Enlightenment, and again, the same question with that - why not allow Compiz to inherit the window style from whatever WM is running, and also allow for it's effects, without having to use a full Gnome or KDE session or have to use Emerald?

Because not all of them have seperate window manager and panel components. For example simplistic window managers like FluxBox and Enlightenment integrate all of their functions (drawing windows, presenting the UI, etc) into one single binary, so there is no window manager to replace.

Larger environments like KDE, GNOME, and XFCE are made up of many smaller processes so that some of them can be stopped or replaced without killing the whole system.

KDE, GNOME, LXDE and XFCE are desktop environments. They have API's and additional services. They also include a default window manager, which can be replaced. Openbox, Fluxbox, Windowmaker, IceWM, etc. are window managers that can replace the default window manager in any of those desktop environments. Compiz is also a window manager and was designed specifically for that purpose. It would not be possible to "replace" Openbox's window manager with Compiz.