I seriously doubt the authenticity of this report BUT.. if it is true, this could have something to do with Manhunt 2.
In the past, Nintendo has disallowed M rated games on their systems... they wouldn't even let the original Mortal Kombat be released on SNES unless they got rid of the blood. It is very possible that Nintendo told Rockstar they wouldn't allow Manhunt 2 on the Wii under any circumstances.. I'm sure that would hurt their business relationship quite a bit.
Perhaps Sony allowed Rockstar to release Manhunt 2 (in its current state) on their systems as part of a trade off. It makes sense, because Rockstar is not currently in the position to lose a ton of money (which they will if Manhunt 2 is not allowed to be released.)