The Logitech Quickcam Pro 4000 would not run without crashing on my Mac Mini under Leopard 10.5.1 even after installing the latest Logitech driver (8.0.1),
I was pointed to
http://webcam-osx.sourceforge.net/ and got a free download driver that fixed the problem
https://forums.macrumors.com/threads/416779/
The cam now works, but it is not nearly as functional as it is under Windows. Very little software control of the camera.
I ordered the Creative Live! Cam Optia AF which claims to be OS X friendly, but it hasnt arrived yet.
I went to check out the discussion you posted a link to for the history of your situation, but it only took me to this same discussion, so you might have gotten the wrong link.
I do believe what you are saying. But, I think perhaps the reason it worked is not because MacCam is the complete solution, but rather that you had a combination of situations that made it work.
MacCam only enables the camera to work in OS X. It does not enable the camera to work in iChat. The situation with iChat is a different issue. It has nothing to do with whether the camera works in OS X. iChat has it's own set of requirements and cameras that it will work with.
So, for those with cameras without OS X drivers and those which are not UVC compliant, then you would use MacCam to enable the camera to work in OS X.
Beyond that, you need to enable compatibility with iChat (unless you don't plan on using iChat). To establish compatibility with iChat, you then need a piece of software to bridge that compatibility issue. The most common solution is the $10 shareware program mentioned previously. But, in your case, I suspect that one of the following may have happened:
1) You used a IM program other than iChat (such as AOL, Yahoo, Microsoft Messenger, etc. - although I don't know how many of those support video chatting).
or
2) You mentioned having software installed that came with the camera for OS X. Perhaps, that software was deficient in enabling the camera to work with OS X. And, that's where MacCam came in and resolved it. But, suppose further, that rather than employing the shareware solution for $10, that the other portion of the software that came with your camera functioned enough to bridge the compatibility issue with iChat.
Essentially, the compatibility with OS X being handled by MacCam, and the compatibility with iChat being handled by the software that came with your camera which was probably still installed.
That's just my guess.
If the camera was already UVC compliant, then it would not have needed either MacCam or a solution to enable compatibility with iChat.
But, if it's not UVC compliant, then either you weren't using it with iChat, or I suspect you may have used another IM program.
Or, perhaps something weird just worked in your situation
All I know, is that a UVC camera will plug in and work fine without anything additional. And, that a camera that isn't UVC compliant will need something more than MacCam to work in iChat (they clearly indicate that on the MacCam site, and I tried it with my other non-UVC compliant web cam just hoping they were wrong).