It's not that gamers are getting dumber, but rather, as more of the general population overlaps with the gaming population, dumber people are playing video games. It seems like there're fewer "smart" games out there now, but really there's probably even more, they simply don't get the kind of face time (and don't have decades of small but vocal groups of people singing their praises, by simple virtue of not having been around as long,) as the major players do. The composition has shifted, but that is true of any creative industry as the market value goes up.
That would be like looking at early cinema: Kurosawa, Orsen Welles, French New Wave, and putting it against Michael Bay and saying, "are movie-goers getting dumber?" Which, well, yes, (and as more shitty movies make bank, there's more incentive to make shitty movies, and thus more saturation and conditioning of the public to appreciate that kind of thing,) but the "creative intelligentsia" will always be able to thrive off the leftovers of the larger industrial beast and fantastic and brilliant new material will continually come into light as long as there is variation in the population of the species (finding the best of it though, will always require a conscientious effort on the consumer, and most likely an intentional refining and adjustment of taste. The best works are often quite difficult to digest, and the challenge of doing so is implicit in the reward.)
