Wiki + permissions = Enterprise Content Management (ECM)?

Wikis are in essence free form information editors, I.E. they are very good content management devices. Wikis usually have multiple authors, so some servers need/use permissions to control malicious editing, but few seems to have added read permissions. With read permissions the wiki may become viable at an enterprise level where there is a lot of sensitive information. Enterprise level software can cost lots of money (read: big opportunity for Wiki software companies), so why aren't there Wiki ECM solutions running around (Hint, hint, hint)? Certainly there are some challenges (search over permissions, granularity of permissions, how to convince customers they want this product, etc), but they've already been solved by many companies. Perhaps wikis are just too new...