Why does his claim sound so preposterous to you? I think it's very probable. Price does matter, as price is one of the things that hobble the PS3's sales (in past eras, it's what rendered the Neo Geo a niche platform for only the the wealthiest gamers). Had everything else been identical (specs, etc.) but the PS3 cost $350 and the Wii $400, then I do think the PS3 would have sold a lot better and the Wii a lot worse. And the "Wii audience" is are largely gamers with no particular brand loyalty. Many if not most gamers, especially in America are "swing voters" that all the major brands are competing for. Nintendo wasn't just offering quality games and new ways to play games, but they also offered it at a bargain price. Being the best value for one's dollar is what drove people back to Nintendo, not an influx of "casuals" or any of the other common theories.

Then again, this whole scenario isn't very realistic to begin with . The PS3 didn't really have any killer apps until late 2007 when games like Uncharted debuted, so the lower price would have helped only so much, perhaps only enhancing the first year of two of sales by a few million units. Also, SCE would probably have been crippled as they'd be bleeding $450+ per system sold if they sold a system that cost over $800 to make at less than half that, so a $350 PS3 would have likely lacked Blu-ray and been less powerful than what it was. Also, if the Wii did cost $400, it would have been a lot more powerful than it was, perhaps being sufficient to draw in third-party developers, thus causing big games like COD, Assassin's Creed, and GTA to be split three ways as all the systems would have been roughly on par with each other. This in turn would have resulted in the Wii still selling well today due to a better selection of games and solid long-term support, perhaps even being on track to surpass the PS2.

That would be the one and only way I'd ever purchase one.  I'm hoping.