I've seen studies like this, maybe not with video games but with TV content or whatever, going back at least as far as the Nixon era. Come to think of it, even in the 50s when I was a kid there were complaints about the influence of Rock and Roll on children.

Apparently its a political culture thing. The self-appointed guardians of morality assume there's a connection and, I think it's a reasonable, legitimate concern. So yes, a study is justified. My problem is that when the study gives answers the guardians of morality don't like, they reject it. I mostly remember there was a big stink during the Nixon administration when one of these studies didn't give the conservatives the answers they wanted. (BTW, I think liberals are just as prone to get in a snit when studies don't support their preconceived notions either. This is a Human Nature thing, not a liberal vs conservative thing.)

So, there is a motive to fudge the results to give the sponsors of the study the answers they want.