I don't think the inability to directly measure audience is much more of a problem for satellite content providers than it is for AM and FM broadcasters. About all they have to work with is Arbitron and the like, which is pretty dicey for smaller markets. At least the satellite broadcasters would have national data.
I have thought for some time that XM and Sirius are likely to start leasing channels, or even timeshares of channels, rather than to keep trying to fill all their channels themselves. Some of the content looks a lot like that now, although I have no idea what the business arrangements are.