480i is standard.. even in 4:3 mode, it's running 480i. GT4 is the same. 16:9 simply changes the pixel aspect ratio so that it fills the screen of a widescreen TV. If you don't have a widescreen TV, it's worse than useless.
You're welcome! And yes, widescreen is nice because each player ends up with 8:9 rather than 4:1.5. This makes everything significantly more enjoyable (: