I believe that line in WoWWiki is a misinterpretation of this paragraph,
We do not allow add-ons or expansions for Diablo. You may make and distribute StarCraft and Warcraft maps and campaigns that you have created yourself, so long as it is for personal, non- commercial purposes. Any such maps or campaigns would also be subject to the other terms outlined in our End User License Agreements included with those products.
This specifically does not mention World of Warcraft. As i recall, unlike other companies such as Bioware (for NWN mods), Blizzard does not claim ownership of AddOns written for WoW (as long as you write the code yourself and don't package their copyrighted images or sounds or what have you along with them), and as far as i know, you are free to do what you wish with them.
However, this is probably something you should be sure about before you go licensing your addons, so i recommend contacting Blizzard's legal department and asking them.
edit: I have, for the time being, removed that line from the article, adding of course the appropriate reasoning to the Talk page.
You can charge for the "access" to AddOns, but afaik not for the AddOn itself(in the end its totally the same for the user).
To prevent them "pirating" the AddOn you can Watermark each mod somehow and track down people distributing it elsewhere by banning their accounts etc.
In the end its useless though as everyone wanting to get the mod will get it somehow :)
If you program a good Page with easy uploading mechanism (for example from google code SVN or whatever SVN) including a seperate updater that updates all AddOns you might be able to charge for it. The problem is no author would allow you to use their AddOns to earn money :)
I dunno about you, but WoW itself sucks up a good bit of time.
You can sell copies of the addon as you wish yes. But it's not likely to sell. What you should instead do if you feel you're spending too much time on addons and would like at least a little compensation for your work is add a donate link to whatever GUI or slash-command your addons may have and to the download pages as well. If your addons are useful and effective and enough people like them, you'll get donations.
As i understand, there is such a thing as compiled Lua, but Blizzard has disabled its function within WoW's engine, possibly to ensure that you can't distribute addons that do underhanded things without somebody noticing.