I can't think of a BD player that doesn't play CDs. They are not any better at it. Considering the fact that most of them have slower load times they could be considered worse. It's more of the convenience of having one player that does it all.
The higher priced players, aside from having more bells, whistles, and format capability, generally have better video processing chips. Whether or not the difference is visible is debatable and depends on the display they are viewed on.