your reasoning is bad, and you should feel bad.
The Wii audience (the 100 million you point at) was only actually relevant for a very brief period of time, and most major publishers never really managed to leverage them.
EA, Ubi, Activision, Square Enix, Capcom, etc have been targeting the PS360 audience exclusively for years now, because the Wii audience was notoriously unpredictable and did not buy the games that the industry had been geared up to produce. It's YOY sales that matter here, not "generation over generation." Exclude nintendo's offerings (wii fit, wii sports, etc) and you're left with only a few dance games doing any kinds of numbers. Your calculations also ignore that PC has exploded with Steam, and is way, WAY larger than it's ever been while catering to the same audience as the PS360.
The core gaming audience (the one that was present on GCN, Xbox, and PS2) grew last gen, it didn't shrink, and all indications are that it will continue to grow with the record breaking launches of the PS4 and XboxOne. If you're a nintendo only gamer you might not be too pleased, but that audience has been shrinking generation over generation since the NES.