The highlight issue is one I've seen make some themes (that look great in screen shots and on most views when loaded) very hard to actually use on a daily basis.

Allowing for differences in screen size (Pearl, Curve, Bold, etc.), eyesight, and ambient conditions means that theme developers need (I believe) to fall more on the side of clarity and ease of reading (when dealing with highlighting) than 100% faithfulness to a theme color scheme...just my two cents.