Share of Sirius XM Radio (SIRI 0.98%) opened slightly lower -- and Pandora (P) moved sharply down -- after Apple (AAPL -1.22%) revealed impressive early adoption of its iTunes Radio streaming platform. 

The consumer tech giant announced that the free Internet radio service attracted 11 million unique listeners since rolling out last Wednesday. 

It's a big number, and it's the kind of stuff that is leading the market to question the vulnerability of Sirius XM's more than 25 million subscribers and Pandora's more than 72 million monthly unique listeners. 

However, there are also some pretty good reasons not to worry about Apple's initial performance. 

For starters, let's consider that iTunes Radio became part of Wednesday's iOS 7 rollout that has reached 200 million converts according to Apple. In other words, we're talking about less than 6% of the iPhone, iPad, and iPod touch users who updated to iOS 7 even bothered to check out the offering.

We also don't know how engaged they are. 

Apple bragged about a million iTunes users registering for Ping -- Apple's short-lived shot at social music -- during the first 48 hours of availability three years ago. It didn't last

Yes, 11 million listeners is more impressive than a million iTunes users registering for a poorly constructed social-sharing platform, but we don't know how many of these people will actually stick around. 

Pandora served up 1.35 billion hours to its 72.1 million unique visitors last month. That breaks down 18.7 hours per listener over the course of the month. Is Apple achieving this kind of stickiness or are folks just tuning for a song or two and moving on? How many of these 11 million listeners came back a second time after kicking the tires? 

We'll know if iTunes Radio is making a dent in Pandora and Sirius XM sooner than Apple may be willing to tell us. Pandora reports its metrics monthly, and we're about two weeks away from getting a snapshot of how it's holding up in September.

Sirius XM's quarter ends this month, so we'll be getting a quarterly report in a little more than a month.

Don't be surprised if Pandora and Sirius XM are doing just fine. Pandora recently scrapped a usage cap for mobile users of its free ad-based service. Car sales have been strong, paving the way for another quarter of healthy subscriber growth at Sirius XM. 

Sure, it's true that placing iTunes Radio front and center for iOS users may eventually eat into the audiences of Pandora and Sirius XM in this era where connected cars are a growing in number. However, Sirius XM was able to grow throughout Pandora's explosion in popularity.

We also don't know if the folks checking out iTunes Radio are new to streaming in general. After all, we're talking about iTunes Music users, who may have been leaning on the music stored on their iTunes account in the past. If iTunes Radio educates iTunes Music users on the merits of streaming, it wouldn't be a surprise to see Pandora and Sirius XM benefit from the musical awakenings.

Today's market action may not indicate that iTunes Radio will be more friend than foe to Pandora and Sirius XM, but there are too many unknowns to assume that the two premium radio leaders should be punished here. The sell-offs today appear overdone, and it wouldn't be a surprise to see the market change its tune once it realizes that Pandora and Sirius XM can turn up the volume in a few weeks.