It's for the PC.So people without a Wii can experience the SMG gameplay.
Besides,its not a complete rip off.It just shares the same gameplay mechanics but has different enemies and characters.It does copy a lot of ideas from SMG though.
It's not nearly as bad as I thought. It's obviously heavily influenced by Galaxy, but a lot of games influence other games. A lot of people probably can't tell the difference between Unreal Tournament and Quake 3 (bad example, I know).