Bringing them both to the same level creates the same problem Apple used to have... many (including myself) can easily justify getting MacBook instead of the MacBook Pro because the MacBook does everything you need the Pro version to do.
Sigh. The MBP offers a lot more than a faster CPU. Larger screen, dedicated GPU, better I/O, backlit keyboard to mention a few things. The MBP is a portable workstation and the MB is a notebook.