I would say it has expanded the market, but at the family level, that is, more people of the family are playing it than did the PS2. Primarily you know this because of the games of Wii Sports and Wii Fit are more universal to pick up and play than probably any PS2 game, not to mention the ease of the Wii controller vs a 'standard' controller.
The other thing we don't know is how many of the GC and Xbox owners also owned a PS2. If all of the GC and Xbox owners that have now purchased a Wii, had owned a PS2, then they are already 'counted' in the 8M. And the 3.4M would be all new gamers. Of course, that extreme is unlikely. But say, 25% of the GC and Xbox owners bought a Wii, but of that number, 80% also owned a PS2. That means only 5% of the GC/Xboxers (or 1.25M) are ones that bot the Wii, but did not own a PS2. Leaving 2.15M as completely new gamers. About 20% of the total Wii gamers.
Torturing the numbers. Hear them scream.
