Actually, it is. a mature industry (as gaming is) does not grow by 10 or 20 percent YOY. The growth is going to be more organic, and mirror population increases.
Mobile is growing much more quickly, because mobile is an immature industry. it's still reaching people who have yet to be reached, but it WILL slow down. anyone who thinks apple and android will still be growing at the rates they are now is in for an extremely rude awakening.
This goes back to what I said before. Wii gaming was most certainly an anomaly- it branched gaming out to a new audience, but this audience wasn't sustainable. you had people buying the system for wii sports and wii fit, who were never going to buy a console again. They were in for the novelty, and once satisfied moved on.
This kind of audience isn't exclusive to gaming, it can happen anywhere, and trying to build a business around them is suicide.
The core audience has grown generation over generation every year since the crash of 1983. there is no possibility for contraction, especially since (as I pointed out) MS and Sony aren't launching in the middle of a worldwide economic collapse this time.