Anyone remember the mazzlegasm? Two years ago there was an addon for World of Warcraft called MazzleUI which to advertise itself had your character /yelling "I've had an intense Mazzlegasm" across the entire zone, and many of the users of that addon didn't find that funny. WoW addons can do nearly anything you can do, including things your personal code of honor or decency wouldn't let you do. For example it would be easy enough to have an addon send a whisper advertising some gold-seller to everyone on your friend list and in your guild. So obviously there are acceptable and inacceptable uses of the power of addons, and somebody has to make rules where the line between those is. Blizzard posted the rules last Friday, and not everyone is happy. Because besides the obvious prohibition of offensive content and gold spam, the rules also make it harder for the addon authors to make money. Addons must be free of charge, may not contain hidden code, may not advertise themselves in game, or ask for donations in game. Authors are still allowed to ask for donations on their website, but they say that isn't enough.
The author of Outfitter has gone on strike and withdrawn his addon, and action which would have had more significance if upcoming patch 3.1 wouldn't make Outfitter obsolete anyway. The author of Questhelper says he currently making a full income from donations, and might not be able to keep that up if his addon doesn't ask for donations in game any more. And of course there is Carbonite, an addon you need to pay for to use, which recently developed a "Free2Play with advertising" version, which is rumored to have sparked Blizzard's new rules.
I think the Outfitter example shows well that addon authors never had many rights. Like so many addons before it, Blizzard is simply introducing the addon functionality in the standard UI in patch 3.1, making the addon obsolete. I wouldn't be terribly surprised if some future patch introduced functionality to WoW similar to Questhelper's one, other MMORPGs like WAR are already marking quest locations on the map. So relying on income from an addon was never a really good idea. But Questhelper was downloaded over 20 million times from Curse in its various versions, and the author rightfully claims that his addon has more users than many MMORPGs. Shouldn't that give him any rights? No, legally it doesn't. Because his addon piggybacks on World of Warcraft, and would be completely worthless without WoW, Blizzard is the sole holder of any rights. Blizzard can change the LUA addon language at any time, or even disable it.
As some readers noticed, the problem is that few people play without addons, and addons have become increasingly complex. Even the players who constantly complain that WoW isn't challenging enough have their addon directory loaded full of little programs that make raiding much easier, from threat meters, to addons warning of boss abilities, to healbots. Players have become too dependant on these addons, and now authors threatening to withhold them pose a real threat. But us having become addicted to addons doesn't really give the addon authors any rights, only some power to inconvenience us.
I don't think addons were supposed to get this complex, or to make their authors rich. Blizzard was allowing fans to add to the game, and not people to make a living with unauthorized secondary WoW products. So I find the rules they did set up quite reasonable. If those rules decrease the income of the addon authors, thereby preventing them from working on addon full time, and thus limiting addons to smaller, less complex things, that could ultimately be better for the game anyway. The "convenience" of addons might already have gone too far, removing some vital game elements and making WoW too trivial. I wonder if people would still find Naxxramas "too easy" if they would run it without any addons.