I tried to make sense of how all these disparate technologies fit together. Give it a read if you like (CC-licensed):
http://www.polberger.se/components/
OSGi seem to push the concept further and try to define how plugin should integrate in a hosting application (ex: eclipse ID plugin, web browser extension ...) The way OSGi try to achieve this is by defining protocol for dependency injection (Services Registry, Modules, Life-Cycle inteface ..)
I never really understood COM, I built some OCX module for visual basic 6. I have been told OCX are ActiveX control and that ActiveX control are based on COM but this is all confusing.
In the end, it doesn't much matter. I chose a topic for my thesis way back in 2005, and at that time, there was some academic interest in what was called Component-Based Software Engineering (CBSE). That interest, as far as I can tell, evaporated pretty quickly.
If memory serves, XPCOM was fairly derivative of COM, but fully cross-platform. (It had to be, as Netscape's browser and its open source successor ran on Windows, Mac OS and lots of different Unix flavors.) For this reason, I didn't include a full section on it in my thesis, but I do mention it in passing.
XPCOM saw overuse in the codebase, which led to bloat and a years-long effort to cut down on its use[1]. However, when I studied XPCOM, it seemed like an excellent way to bring the core ideas of COM to a cross-platform codebase, with C++ and JavaScript language bindings.