There has been much discussion on this forum on chromatic aberration and, whether it is caused by objectives or eyepieces.
I stumbled across this article, http://www.cloudynights.com/item.php?item_id=82&pr=3x75 on Cloudy Nights and it would appear that there is a significant third source of CA - prisms.
All binoculars have, of necessity, a fast focal ratio and most birding scopes are around f/6 to keep overall length down. This means that light rays near the periphery of the objective are meeting the prism at an angle and being dispersed.
Dielectrically coated mirrors for straight-through viewing (Porro equivalent) would probably be enormously complex and costly. The surface finishing requirements for reflectors are even more exacting than for refractors if scatter and loss of contrast are to be avoided.
I don't know if there are varieties of glass suitable for prisms with a similar refractive index to BaK4 and less dispersion, but it would appear that designers have to settle on a compromise of conflicting requirements and that we shall probably not get much closer to optical perfection.
John