1 : There is a 30 day exclusive period from the point a track hits the in game music store on 360 before it can be made available on other systems.
2 : Select tracks will be making their way to the other systems after said amount of exclusivity has passed.
Exactly. Sit back and wait. Not many here will understand what is invovled with Nintendo/Sony in getting stuff through QA before release. The tracks and charts are ready, so it is not as if there are any extra overheads as with regular DLC.
Speculation on prices and timeframes are little more than that.