There may indeed be more negative messages in the mediasphere today, but that's not the only way to evaluate whether TV and games are having a positive impact. Just as important, if not more important, is the kind of thinking you have to do to make sense of a cultural experience.
There is evidence for both sides. There are some righteously dumb arses around, and plenty of pap for them to suck up, and yet there is also this world of complex nuanced information which we negotiate for fun and profit. And in some ways our standards, for speed and complexity of data input, are higher than ever before.
On the other hand speed and complexity of input are value-free characteristics. Crap ideas can also come fast and complex. Like working out at the gymn, your brain has to work, perhaps it builds its strength, but it doesn't necessarily go anywhere. But it might, one day, if you get the chance. You are prepped and ready.
One final thought. Are books like this good or bad things? Would it be better if senior people in my organisation were using deeper and more academic books to guide their thinking? Or have academics deliberately placed themselves beyond such use? The book is a symptom/product of the system it lauds. To present relatively complex or innovative ideas in a simplified ad-speak format: is this dumbing down, or dumbing up?