Absent from the new Sirius app are a number of the broadcaster’s more popular channels, among them Howard Stern’s, which Sirius often claims are responsible for driving more subscriptions than any other. Also missing: MLB Play-by-Play, NFL Play-by-Play and Sirius NASCAR Radio.

That the company calls this app “Sirius XM Premium Online” when it fails to include much of the broadcaster’s more popular content is ironic. That it expects subscribers to pay an additional $2.99/month to access it after a week-long free trial is silly (Note: If you are already a Sirius XM Internet subscriber or subscribe to the company’s Premium Online service, Sirius waives that fee). Without Stern and those other channels, there’s really no reason to. There are far too many other ways to listen free music on the iPhone that don’t require a monthly subscription fee–Pandora, for example. Or Last.fm. And NormSoft’s Pocket Tunes app has been streaming Stern for months now.

Surely, Sirius knows this. So why not include Stern et al? Did a rights issue prevent Sirius from doing so? Did it convince itself that Jimmy Buffett’s Radio Margaritaville and Oprah Radio were compelling enough reasons to download the app? Or perhaps the company is planning a standalone Stern app for which it will charge separately. Or maybe Stern is working on that himself.

And seriously, doesn’t Sirius XM pay Stern too much not to include him?

In any event, the app is an enormous disappointment. Which is too bad. Because Sirius really could have used the few additional subscribers Sirius XM Premium Online might have attracted. With the souring economy weighing heavily on the auto industry–-a mainstay of Sirius’s business–-and partner Chrysler navigating bankruptcy, the struggling company is bracing itself for nasty subscriber losses this year.

If this is all that Sirius XM has to offer on the iPhone, it would have been wiser to do what Netflix (NFLX) did with its Watch It Now online streaming service–provide it gratis to active subscribers as a loyalty bonus. Without Sirius XM’s top-tier content, there’s little to differentiate its iPhone app from Pandora and Last.fm. And Pandora and Last.fm are free.

UPDATE: A quick review of the Sirius Internet Radio FAQ reveals that it is indeed licensing restrictions that prevent Sirius XM from offering NFL, MLB and NASCAR via the Internet and presumably via the iPhone as well. Those same restrictions, however, do not seem to apply to Howard Stern’s channels, which all appear in the Sirius Internet Radio lineup.

UPDATE: Sirius XM has declined comment on the Stern issue beyond what was already said in this morning’s press release.

Announcing the debut of Last.fm’s “unprecedented” on-demand music streaming platform, Jones–in a moment of Zuckerbergian grandiosity–proclaimed:

Today we’re redesigning the music economy.”

Which will no doubt come as a bit of a surprise to Apple, and Real, and Amazon and, above all, Imeem, which announced a similar ad-supported service last month.

To be fair, Last.fm’s free on-demand service seems a bit more compelling. Certainly, the CBS-owned site is the only one among the few to offer access to music from all four major labels and a host of independents to anyone willing to stare at an ad for while. And providing complete album streams on a “try before you buy” basis is truly a nice touch.

Still, Last.fm does have one significant limitation: You can listen to a track no more than three times unless you agree to pay for the subscription version of the service or purchase it from an affiliate. Will that be a deal-breaker for the average music fan or a good reason to buy your music through Last.fm, rather than iTunes? Hard to say. “The free-music-on-demand field has been a tough one, with many announcements but few real entries (consider, for example, the often-delayed Qtrax and vaporous Mashboxx),” notes the Los Angeles Times’s Jon Healey. “With CBS’ backing, Last.fm might be able to search longer for a workable formula than the typical start-up. But at some point, it has to find a way to pay the bills.”