SiriusOwner: Do you realize what it takes to get a car manufacturer to change out factory installed radios? First they have to be tested to make sure that the power use and heat production is not significantly different than the current radio in there. If it is, they have to make adjustments and then retest.
There are also contractual obligations that have to be considered. GM has a contract to install XM radios. Will that contract get changed? It would have to be at the consent of both the SIRI and GM... but do you think GM is going to want to change things in the middle of production? Not unless there was something in it for them, especially with the way their business is operating right now.
Perhaps you will start to see changes in the 2010 model year, but I would not really expect to see it before that. Even that is stretching it somewhat...