where do sites like curse (wardb) get it's item data?

all player submitted? directly from mythic?

if so is there a way to share this data via some API?

I have a project I am working on and recompiling all the in game items seems silly if someone has already collected it.

wardb, wowdb, and wowhead all get their data from users. In the first two cases, if you use the Curse Client with the Curse Profiler addon installed (it is on by default, but you can disable it) then it automatically uploads when you are done playing WoW or WAR. WowHead uses its own client.

http://wow.curse.com/client/ http://www.wowhead.com/?client

You will have to contact the people at wowhead to get a data dump database addon. As for wardb and wowdb, I would think Kaelten is the man to ask.