It looks like Sega will be releasing the MadWorld soundtrack on 6/30/09 for all to purchase. The soundtrack will be available at Sumthing Distribution as mail order or digital download. Platinum Games was nice enough to post a video so you can get a sense of what the tracks are like:

I hope things continue on this front because there are some truly amazing pieces of work in game music from lyrical pieces like in MadWorld, or beautiful strings in Heavenly Sword to majestic tones of Shadow of the Colossus. Keep releasing those soundtracks because I will keep buying!