It's only half over, but this has already been a bang-up week for satellite radio. In a Monday announcement that seems to have surprised the Street, XM Satellite Radio (NASDAQ:XMSR) reported having reached 2 million subscribers. Milestones like these are, of course, meaningless.

Does No. 2,000,000 really mean more than No. 1,999,999? Of course not. But what is worth noting is that XM had 1.68 million subscribers as of March 31. That means the firm added nearly 320,000 listeners to its ranks so far this quarter, and there are still a couple of weeks to go. Sound pretty good? That depends on your point of view.

In absolute terms, the quarter will end with a better raw subscriber increase than the first quarter, when 321,000 were added. However, in terms of growth rates, last year's second quarter ended with a 43% improvement over the first quarter. XM would need to hit 2.4 million subscribers by the end of June to match that blistering pace. It's not going to happen.

The growth is still impressive, but given the number of satellite radio investors who send me angry email citing hyper growth rates, it bears mentioning that the days of 50% quarter-over-quarter growth disappear quickly. Place your bets accordingly.

Meanwhile, Sirius Satellite Radio (NASDAQ:SIRI) is lighting fireworks of its own this week with the National Rifle Association's (NRA) announcement that it will launch programming on Sirius' airwaves. The NRA's move is actually a tactic in its ongoing battle against legal limits on soft-money contributions and political advertising.

You might wonder why Sirius would want to provide the teapot for this tempest, and the press-hungry firm has actually made the rare move of not commenting on the story. I say Sirius should embrace it. After all, the only bad PR is no PR at all. Moreover, opponents can't do much grousing because Sirius provides plenty for left-wingers to like, including NPR and Air America. In fact, it's crazy moves like this that make even a Sirius skeptic like me admit that the firm might have a content advantage over XM.

For more Fool coverage of the satellite radio biz:

  • See Fools slug it out to decide who's king of the hill.
  • Is the NRA show just another way for Sirius to woo the men?
  • Join other Fools in the Sirius and XM discussion boards.

Fool contributor Seth Jayson has plenty of guns, but thinks NRA might stand for Non Rational Americans. He owns no company mentioned. View his Fool profile here.