Define "large".
That's a tough one. It can handle Crysis?
Erm, I know, here's my new benchmark: my mum wouldn't need digital foundry to see it looked better!
The thing about that comparison is that we don't know the threshold of what the GC or Wii could handle. Wii's TDP is comparable to some tablets and it clearly has more space to work with. And like I mentioned they added (so far) a couple of smaller vents.
The GC had vents too. Looking the inside of the Wii and the GC, I'm guessing that the Wuu is supposed to draw air across an aluminium heatsink like the Wii, only a larger one than in the Wii. Maybe they can increase cooling efficiency over the GC by making the fins higher, closer, thinner and using a wider sink as in the Wii, but it'll still have to be quite a lot shorter. The position of the intakes relative to the exhaust looks strange, as air won't be drawn directly and evenly across the heatsink as in the GC and Wii. Maybe it's a temporary thing, or an interesting arrangement of heatpipes or something.
Any tablet with chips as hot as those in the Wii would not be passively cooled, and would be a thick and (under load) noisy beast probably running Windows 7 on an x86 processor and likely using one or more heatpipes. It wouldn't be the iPad kind of thing that most of us now think of when we talk about tablets.