Is there a reference to back this claim up (PS2 part)?
For all I know, wii casuals are moms and grandmas.
There is casual, and there is casual.
Does it really need backing up? It's just common sense. There's plenty of overlap between what was the ps2 market and the current 360/ps3 and wii markets. While there maybe some brand loyalty I have no doubt that many former ps2 owners are now quite happily wii owners.
It would be interesting to see a study of current wii owners and their previous consoles. While I don't doubt that the wii has brought a number of first time console owners into the video game market, I still think it would be a small minority (perhaps even less than 10%) of them.