I thought the whole Curse and WoW Interface vs WoWMatrix scuffle was over, but the people at WoWMatrix have just fired back an "FAQ" giving their side of the story. I put FAQ in quotes because I'm not sure these are frequently asked questions so much as questions Matrix frequently wants to answer, but that's OK. I like the format.
Here is the situation as they put it: The Matrix people are respecting Curse/WI's demands that they quit using Curse/WI bandwidth, so as of now you can only get addons through WM that are hosted on the WM servers. They are hosting addons on their servers that the authors asked to be hosted there, or that are distributed under a free license (such as the GPL) that allows such re-hosting.
And now it starts to get contentious. Curse and WoW Interface claimed that WM was almost completely unresponsive to any kind of communication they tried to make, which is what forced them to take the drastic measures they took. WM, on the other hand, claim that Curse refused to negotiate and instead just tried to buy Matrix outright, whereas WM was trying to compensate for bandwidth, figure out how to use less bandwidth, and show Curse ads.
Basically, WM's side of the story is that they tried everything they could to work with WoW Interface and Curse in order to provide a single solution that was best for the user community - to quote them directly, "both Curse and WoWInterface are more concerned about their own profits than working with us to help better serve the gaming community."
This is, again, directly contradictory to what the Curse/WoWI release said, which is that Matrix showed very little interest in working with them, making only a token lowball offer to compensate for bandwidth, and just wanted to go on leeching, basically. Obviously at least one side is misrepresenting facts, although it's impossible to say which one.
On a final note, if you want to help the WoWMatrix folks, they encourage you to submit any addons that you want added that are under a free license, so that's one thing you can do to build their database.[thanks, Chias]