We have to be careful about something here. If I'm not mistaken, we're trying to use consoles sold as a reflection of total audience size, right?
That's good if you want to look at big picture numbers and say, "yes, the audience has definitely expanded." Especially since the PS2, then of course the huge handheld market (mostly (3)DS).
However, we mustn't split hairs or risk losing the point of the conversation. Yes, the PS2 is still selling, but how many of those are new customers? How many of those are people replacing broken systems? How many of those are old customers upgrading to the sleek, sexy, and space-efficient PS2 slim?
What about the 360? How many of those are re-purchases from RRODs?
What about for the Gamecube? How many of those were purchased after its generation and duct-taped together to form the Wii?
ahhh see? A sense of humor is good.
Anyway, what I'm getting at is, there are too many variables (as Optimus was beginning to summarize) so if we want to look at the big picture? Fine. But beyond that it's very shaky ground.
Is the industry growing? Especially since the PS2? Based on my observations: yes.
Can it grow beyond this point? I believe it will eventually, but I think it will be more due to gamers getting older and new generations joining them. I don't think we will see another "expanded audience" like we did with the PS2 and Wii anytime soon.