Ubuntu One Music Store Available for Download
crenk.com
crenk.com
Since the files are the same and there's no need for duplication on UbuntuOne's servers why would they need to charge you for storing them on their servers?
IANAL but it seems like this would make the data _yours_ instead of them providing it as a streaming service. Which means if they are e.g. forced by a court for whatever reason to not provide a specific song anymore (if the author plagiarised it for example), they can't take it away again from you because it's yours. If it were a simple service you could access to get a copy, they might be forced to not provide that anymore.