well, the original question was could we use mice for games such as minesweer/bejewled. and those games to my knowledge are downloaded from xbox live itself. there is no reason why they cant program mouse support for these games or for the xbox360 interface since theres gonna be tons of connectivity to the xbox360.
and theres no reason why they cant program IE or something to use on Xb360 since theres already internet connection available.
on the games issue, mice vs controllers theres no real disadvantage if you practice. i play PC FPS'S and im fairly proficient with a mouse but not real good at it. a good FPS player on XB can beat me using a controller. its not about mice being more accurate or whatnot, its all in your skill.