I've been gaming since I was about 4. I think anything I'd say would be biased. i don't know how it would have been if i wasn't a gamer, and I never will know. What they need to do is do a long term study of people, from early childhood to early adulthood, have half not play games and the other play games all the time, and watch how their attection spans are affected over an extremely long period of time, like 10 years or something. We need to know the long-term results as well as the short term.
Of course, IDK how they do it, maybe they do what I just exlpained. But in my not-so-humble opinion, I think that my attention span has been either unaffected or possibly improved as a result.