PS3 update:
OK, Harmonix has started putting songs from the Rock Band Network onto the PS3. Unfortunately, they are only able to release 5 songs per week (they will be like regular rock band downloadable content songs).
So they are mostly picking the most popular songs from the xbox downloads which makes a lot of financial sense, but not too much sense to us over here I'm afraid. Keep in mind there are like 240 songs currently in the Rock Band Network. Our favorite two are not exactly chart-toppers :)
Over on the Rock Band forums there are many threads containing tons of posts from Rock Band fanatics requesting their favorites--it's a pretty depressing mix of metal and songs that appeared on earlier games like Guitar Hero.
But buried deep in one of the threads was this post where one of our own fellow KH fans is getting her desires heard, through her husband, who cutely requested both KH songs for her. Here it is, but if you don't want to be a little depressed don't read more posts than just this one :)
http://www.rockband.com/forums/showpost.php?p=3647361&postcount=161
As for you Wii owners, you are really out in the cold rain so far, they still haven't figured out how they are going to get any of the RBN songs out to you.