Good work on taking measures to provide users with a stable environment from which to pull WoW addons. In addition, some simple code to "tag" the IP addresses Wowmatrix uses as they tunnel through your internet/intranet will provide a nice paper trail for your attorneys.
Callling the owners of Wowmatrix with hard evidence in hand and the threat of copywrite - intellectual property infringement is a powerful tool to a) shutdown their actions permanently or b) bring them within operational compliance. This worked for us at Microsoft on several occassions.
Either way...I'm a happy user of both WoW Interface and Curse! My .02.