Hey, I like math. Lets run with some real numbers:
Tip #1 Look at the whole graph (if January isn't showing, they aren't January's numbers
Tip #2 Get America's numbers from January
Wii: 21% / 21M = 1.00% total playtime per million consoles
360: 18% / 16.2M = 1.11% total playtime per million consoles
PS3: 9% / 7.8M = 1.15% total playtime per million consoles
Conclusions:
According to this data the PS3 is played most per console with the 360 3.5% back and the Wii 13% back.
"You can never jump away from Conclusions. Getting back is not so easy. That's why we're so terribly crowded here."
Canby - The Phantom Tollbooth