I don't think there's really any good data stating that Wii JRPGs will outperform PS360 JRPGs yet, but I will agree that I think that can change much faster (and is changing, IMO) than genres like FPS and Pro Sports.
JRPGs aren't necessarily very demanding, in terms of performance, and frankly RPGers aren't so hooked on technical prowess as most gamers tend to be. The JRPG subgenre's dev costs, porting costs, etc. would be drastically different from the FPS costs I posted above. The Wii's costs would be very much on par with the PS360 (not lower), and the porting costs would probably be much less, without serious performance concerns.
If JRPGs are developed primarily on the Wii, I can see a LOT of crossplats happening. I doubt the Wii will ever command enough marketshare to justify JRPG exclusives, except in cases where the developer doesn't have the manpower/budget to do a port at all, and the publisher is Japanese, and primarily only interested in the Japanese market.
