Just did some poking around of the NIMF's website. Interestingly, I could not find this particular warning or anything similar (was there not a similar outcry over Manhunt 2).
The group seems to have its heart in the right place but it is a bit excessive in some of its statements. And it is not one of those groups trying to rid the world of video games per se. And its partners include Microsoft, Best Buy, and ESRB in its GetGameSmart effort)
For example, it says no more than two hours of screen time a day -- that is TV, video games, computers, etc., for children. Not sure what world they are living in as children have had 2x-3x that for years.
It also makes statements without providing evidence/citation that seem right but may not be right -- i.e., studies shown that children with TVs in their do worse in school; M-rated video games have a more profound effect than R-rated movies because of their interactivity (which has been more often debunked than proved, if I recall correctly.
My guess is that this statement is to alert people to pay attention to the ratings (which they talk about and talk about game-appropriateness on their website). Also, it may be that some people think Wii, think family-friendly, and buy whatever. And given the approach that some developers have taken, it is not a surprise that some groups feel that way about consumers as well.
Mike from Morgantown