One thing struck me when these illustrations appeared: these are parodies right? The real artists didn't draw these, right? So it shouldn't be tagged takahashi_rumiko.

Hmm. They're not even writing it with different kanji, it really is 高橋留美子. Would they dare do that without permission?
On the other hand, Takahashi's manga are published by Shogakukan, while Zetsubou is published by Kodansha... it seems weird that an artist would collaborate with the competition.