> we don't want the distribution zip files to get huge

why not? Where do a few extra MB play a role here. I'd rather duplicate jars between the different directories in order to make it easy for the user to figure out what he needs. Hard enough anyways to figure things out, why not make it easier? 

> Everyone else is welcome to dump all the jars in the same /lib directory, we're probably doing already too much with the 3-way division

why? What are you afraid about here?