How is this different than listening to XM Radio Online, which is currently bundled into an XM subscription (i.e., no additional charge). In this case, the BlackBerry is simply another computer that is accessing the XM audio stream. Yes, I could understand a one-time reasonable licensing fee for the XM Radio Mobile application, but $7.99 per month is ludicrous for current subscribers -- a subscription for an additional XM radio receiver is only $6.99 per month!
BTW, XM is not the first to neglect current subscribers when launching a BlackBerry application service. The AAA currently offers no discount to AAA members for their AAA Mobile for BlackBerry application (currently $9.99 per month), which is an "award-winning navigation and local search application from AAA".