Cheesemeister, we may need your help again. ONM is saying that for you to play a digital title, it must be stored on the internal memory of the console itself. So basically, the external harddrives can only store games but you can't actually play them from it. To play them, you have to move them to the actual console itself.
I'm assuming this is a very poor translation on ONM's part, because even on the 3DS you can play games that are stored on external memory.
Edit: They are saying they found this information on
Nintendo's Wii U Japan page.