I feel there are two important factors at work here.
1. The main console in a game players life is fluid. In the last generation the main console remained the PS2 for the entire time and the previous generation before that the main console became the PS1. In this generation mainstream multiconsole ownership is more likely given the fact that all three consoles provide a distinct enough experience that it is justifiable to own more than one. It is also possible to start with a Wii and then buy an Xbox 360 with Kinect or start with an Xbox 360 and later on also purchase a Wii or PS3.
2. Not only has the console market expanded but the presence of a console as a standard part of AV equipment has become a lot more mainstream. Noone thinks twice if they see a PS3/360/Wii sitting amongst your stereo equipment, cable box etc. This is due to both the mainstreaming effect of the Wiimote and later Move and Kinect as well as the fact that both the Xbox 360 and PS3 are relevant as multimedia devices as well as games machines.
Overall I don't think the total number of game buyers will increase over the coming years so in terms of software I think we are probably at or past that peak even as new consoles are sold. Also the reason why the 360 has increased every year is that it had to convince people it was a legitimate alternative to the competing Playstation 3. Contrary to popular belief second place in the U.S. was never in the bag for the Xbox 360 from the start, it was earnt and continues to be earnt every year that the Xbox 360 manages to increase its' sales.
Tease.
