If you look at that Kodak advert in the link I posted, the effect is very clear around the nose. (The ortho image is on the left). So with ortho film, it's hard to 'sculpt' the face and create thinner features or dramatic shadows. Hence the need for retouch.
Here is a shot with a 403 (UV) filter; note the amount of fill. This was in (deliberately) very harsh, direct overhead sunlight. I wanted to see just how bad the skintones would be! The poor gal looks like leather.
BTW xray film has quite a lot of green sensitivity, because (I suppose) it is used to image phosphoresence from a screen, not the actual, direct xray image.
P.S. Ah yes here is a pretty good overview of how xray films work: