There is a lot of misinformation going on here IMHO.
DivX is a video codec (NOT audio; it is video-only). QuickTime, AFAIK, supports DivX codecs. Not out of the box, but you just throw the 3ivX codec in your Library/Quicktime which is easily available and downloable for free from 3ivx.com, and you can transparently watch almost whatever divx content out there (there are only a few problematic, nowadays hard to find, files with the first, now obsolete, divx format, which is very very old now, and even the divx team apostatize).
The main problem with Quicktime and those movies with DivX video is that Quicktime does not fully support the Avi architecture, and note I am not talking about particular codecs, but the whole way an Avi file is supposed to be internally structured, whatever codec it is using. Quicktime decodes their video right away if you have the appropiate codec, which, as I said, is fairly easy to get. The problem is that the audio in those files will usually be in MP3 format, and while QuickTime is indeed able to decode MP3 audio, it is not able to decode MP3 audio inside Avi files. This is like this, wether the video is DivX, Cinepak, Indeo or whatever.
What needs to be fixed, because, mind you, it IS a bug, is MP3 decoding inside avis. It has NOTHING to do with DivX.
If what some of you are asking is off-the-shelf DivX decoding, that is another story, the reason why most people trying to read divx in Macs are blaming Apple about QuickTime is that they cannot HEAR the audio whatever codec/file they download and install in their computers (unless they take not so easy and comfortable measures to translate that avi to a mov). Not a lot of those people would really care if Apple supported that off-the-shelf of not, if not supporting it would simply require to download a simple codec to solve the problem.