I really don't think this hack came from the vWii side of things. They share the same hardware, but the iOS on the vWii are coded specifically for Wii compatibility. Extended memory space and multiple CPU compatibility does not exist in the vWii, so it would have to be coded in by a hacker. And in order for a hacker to code that in, they'd already have to know the inner workings of the WiiU anyway, which can't be probed from the vWii without custom drivers. Its a catch-22.
Hackers have said that the WiiU security chip is just as vulnerable as the Wii's (Starlet). I think they opened the box up, connected some pins directly to it, and started issuing commands. From those commands they learned a software vulnerability, either at the kernel level or at the system menu level, and then exploited from there.
They're keeping things close to the chest for now so as to not ruin the hacking fun for themselves and for everyone else should Nintendo decide to patch the system. Once they have a solid understanding and multiple exploits to fall back on, they will release something.
The reason the vWii got hacked so quickly is because there were multiple IOS exploits that were known to the hacking community, but kept secret from Nintendo so that they were not patched out when they wrote the corresponding vWii IOS.
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