Sirius XM Radio (Nasdaq: SIRI) hasn't forgotten where the accelerator is.

Investors are cheering as the satellite-radio giant boosted its full-year outlook this morning. Sirius XM now expects to close out the year with 750,000 more subscribers than it started with. It sees revenue of roughly $2.75 billion, adjusted operating profits of $575 million, and at least $100 million in free cash flow.

Let's put this into proper perspective by stacking this up against the original guidance that it reaffirmed just 13 days ago.

  • Net subscriber additions would be more than 500,000.
  • Pro forma revenue would be more than $2.7 billion.
  • Adjusted income from operations would clock in at $550 million.
  • Free cash flow would simply be positive.

Some of the new numbers shouldn't come as much of a surprise. Sirius XM rang up $670.6 million in revenue in its latest quarter, translating into a run rate of $2.68 billion -- and that's before the vast majority of new subscriber additions are baked in.

The subscriber-additions projection had been at 500,000 for several months, even though Ford -- and even laggards GM and Toyota -- had strung together several months of healthy car sales. Sirius XM's turnaround over the past year has been tethered to the recovery in the auto market.

Its operating profit and free cash flow are trickier to target, given all of the moving components and the perpetual flux in programming expenses and subscriber acquisition costs.

The only real mystery here is why Sirius XM didn't bump up its guidance when it had the perfect stage to do so less than two weeks ago. The stock went on to fall by 18% over the next four trading days, largely the result of sticking to its earlier guidance despite the obviously positive catalysts.

There are two likely possibilities for raising its guidance now, instead of during its first-quarter report. The first scenario is that Sirius XM truly didn't see the improving trends as potent enough to justify a rosier outlook. The second scenario -- and it's probably the one Howard Stern fans will cling to -- is that negotiations with Sirius XM's most popular celebrity are progressing nicely.

Stern isn't the only reason folks sign up for Sirius -- or tack on the "Best of Sirius" package to existing XM plans -- but he's clearly the game changer. If it becomes clear that Stern won't be renewed when his five-year deal comes up in December, you can be sure that there will be plenty of subscribers who scale back on their long-term commitments to the platform.

In the end, the upbeat outlook places momentum back on the Sirius XM playlist. Pity the shorts who get in the way.

Why do you believe that Sirius XM chose to raise its guidance today instead of when the longs really needed it 13 days ago? Share your thoughts in the comments box below.

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Longtime Fool contributor Rick Munarriz is a subscriber to both Sirius and XM. He owns no shares in any of the stocks in this article and is also a member of the Rule Breakers analytical team, seeking out the next great growth stock early in its defiance. The Fool has a disclosure policy.