What keeps Apple from supporting all IM networks in iChat?

I know that iChat supports AIM, and jabber (along with in-network IM). What keeps AIM off of the other networks? Do the other networks not want to play nice. Is there some prohibitively difficult reverse-engineering process to build in support? Or is Apple just being stubborn on this one.

I would love to be able to use iChat for all messaging. Not just for AIM and jabber. Does anyone know of an integration timeline?