In the SDK documentation there are described two kind of devkits. A CAT-DEV with an internal harddrive and a CAT-R with an optical drive. I think the picture of gudenaurock shows a CAT-DEV and on ebay you get a CAT-R.
Found this on ebay: http://www.ebay.de/itm/Nintendo-Wii-U-Development-Kit-CAT-R-Dev-Kit-sehr-selten-rare-/321789178887?
Maybe interesting for developing a kernel exploit?