This is pretty misleading. The source indicates that it was 46% of 60 stores
in San Diego county. That's way too small and too localized a sample to draw any sort of conclusions about nationwide trends. The 17-year-old loophole is important, too; I certainly wouldn't put it past the groups behind this research to exploit it to help them get the conclusions they want (they clearly have an agenda; just look at their web site), but since there's no mention of their methodology we can't know for sure.
But frankly, even if it this is an accurate representation, it's a big "so what." The whole not selling M-rated games to people under 17 thing is just a voluntary policy that some stores have introduced, but they have no legal obligation to do so (despite what the San Diego East County Youth Coalition wants you to think). A more interesting statistic might be to find out what percentage of the stores had employees that were violating the store policy (if applicable), but the figure would probably be less alarming, so they didn't look into that.
This is obviously just FUD orchestrated to get soccer moms to sign petitions so their local lawmakers can introduce yet another bill trying to turn store policy into law, which will then be roundly rejected by federal judges, just like the
last several times. Pretty pathetic.