My theory is it's in the prism more than the lens.

Either way, seems negligible on the EX1.

one of the biggest problems a video lens has is that it must stay in focus through the entire zoom range. Stills lenses don't need to track focus. As a result video lenses have a lot more glass elements. Also 3ccd designs have to deal with 3 different light paths in the prism. The prism and optical block certain contributes to CA.