The lights are on
I think 2 gigs of memory is lacking also, mostly because of how cheap it is. I am guessing since they are buying directly from the manufacturer Nintendo is paying less than $10 a gig. That said those 2 gigs are not shared with the controller. The controller probably has a built in 128mb of memory or something small like that. Since the controller is not doing any processing it does not need anything else. Just a very small amount of memory to buffer screen data, key inputs, accelerometer data and such till it is transmitted to the console.
Also yes any external USB hard drive or thumb stick should work with the WiiU. Nintendo deserves kudos for that but it does add another $60 or so to the cost of the system. If they are going to start having games with lots of HD DLC the built in console storage will be gone very quick. If/when I buy a WiiU I will pick up a 250-500gig hard drive at the same time.