Gilgex, it's because if you play too overpowered you can end up ruining the show for everyone else. Feel free to go on a rampage, just make sure you show Grimm's weaknesses- e.g. have him be attacked by his own zombies.

Wasn't X-Japan the band that were sued because their name sounded mildly similar to some band in America, even though they were older than that band?