Yes, xm uses two sat in geo sync orbit one on the east coast near the gulf and one near hawaii. Sirius uses three that are in a orbit from south america to canada two are always over the us. As mentioned above they put up repeaters in urban areas with tall buildings, they also sell private repeaters for the house user and stores like best buy and circuit city or malls, etc. BOth offer streaming online of their content.
Having both, xm blows out way more power than sirius and can go through walls, trees, etc. Sirius is more line of sight and since the sats are in orbit the signal can come and go unless you have a range of a clear view. Of course if a repeater is near by that is not a worry, you can get it in basements, cement rooms and even elevelators.
I use both and love both, a search online should get you more information on either and 13 bucks aint that much to ask to get streaming audio from the news channels and commercial free music, anywhere in the us and a few hundred miles into canada, mexico and off the coast.