Remember, they are building a backend and clients for pretty much every platform available, I would say 20 engineers is barely enough to accomplish such a task in a timely manner. 37signal makes their apps available on web only.
Wunderkit was entirely native. There were 0 iOS developers involved in working on Wunderlist with Titanium as you simply don't need native developers for Titanium code (the maintainers in the past were Javascript and front-end developers). I joined as the first iOS developer and worked on Wunderkit. Now all the developers work on the native client. There's also a lot of shared library code between the Mac and iOS team
