I imagine that the posters are implying that the developers of Adium have expressed a philosophical opposition to Apple's iPhone NDA, and so won't join the iPhone developer program. They have a blog, most likely any such state of affairs would be explained there.
That is not it at all. Because of their use of opensource material they have to follow certain disclosure rules which they can't do while under an NDA.
There is no philosophical opposition, simply one placed on them by circumstance.