Good find, I think I got reddit confused with stackoverflow or wikipedia. If there's no clear assignment of copyright to api users, I would imagine that would be problematic for 3rd party app makers.
Isn't this true only if the 3rd party apps are saving the data and/or redistributing it? Apps should be able to request data from reddit just as a normal user would through their browser, since reddit has permission to use (and serve) that content.
Nit: I don't think copyright assignment is the correct term here. That refers to transferring the ownership of the root rights to the material, but you're just referring to granting specific rights under a license.
