I reckon chimps are crap at language because their working memory is too good.
The follow paper may perhaps be (mis)read and bent a bit to support my view 🙂
Decaro, M. S. S., Thomas, R. D. D., and Beilock, S. L. L. (2007). Individual differences in category learning: Sometimes less working memory capacity is better than more. Cognition. To appear.