Very few of the top PS2 games were casual. The PS2 had over 500 Green rated games at Metacritic during its time far more than any other console listed at Metacritic in genres including racing, shooting (the only genre the xboxes have ever had an adantage over PS consoles in), action, adventure, and rpgs. It had very strong appeal to core gamers.
On the other hand, the Wii has the least amount of green games of all 3 current gen consoles by a wide margin this gen.
It's true that many of the core gamers did opt for the 360 earlier this gen (although maybe not so many of those interested in Japanese rpgs, adventure, and racing games did so), thus taking away some core gamers that would have purchased a PS3.
However, the people that held out for jrpg, adventure, and core racing games and the many people that still haven't upgraded to blu-ray would be the ones willing to pick up PS3 / 4 at this point in time.
It wouldn't be enough to allow Sony to beat Wii overall this gen, but it would be enough definitely to have PS3 beat or be on par Wii each year for the rest of this gen which I think would be quite the feather in Sony's cap.
End of gen estimates
Wii -- 100 to 115 million
PS3 -- 75 to 100 million
360 -- 40 to 60 million
