In a bid to simplify music discovery for Twitter users, Twitter today announced a partnership with Apple’s beleaguered Ping social network.

The union will let Ping users publish their activity to their Twitter streams, and it will also let users listen to iTunes song previews and purchase music directly from Twitter’s website. The news seems harmless enough, but I have a sinking feeling that the union isn’t so much about music discovery as it is about turning Twitter’s users into living and breathing iTunes ads.

If anything, the partnership exemplifies the antisocial nature of Ping. Instead of being a resource for finding out what music your friends actually like, Ping seems more focused on telling people what you’ve bought on iTunes and connecting you with artists (so you can buy their music). Now Apple is bringing that commerce-first sensibility to Twitter.

The partnership is also significant because it’s the first instance of Apple playing well with other social networks when it comes to Ping. We previously reported that Apple CEO Steve Jobs showed off Facebook integration with Ping, but once the service launched to the public, the Facebook integration mysteriously disappeared. “Onerous terms” apparently led Apple to abandon the integration, which would have let new Ping users bring in friends from Facebook.

It’s not as if Twitter users don’t have other ways to share music with their friends. You could post a link to any website with music, or use a music-focused service that lets your followers listen to full songs (I like Blip.fm for this). Both of those methods are also much easier than finding a link to a particular artist or album in iTunes, and they also keep your friends inside of a web browser, instead of forcing them to launch iTunes.

The union is also an indicator of just how much Apple is losing out by relying on iTunes as a standalone application instead of making it a web-based service (an issue that could be fixed with Apple’s rumored cloud-based iTunes service). Users can’t buy or preview music on the iTunes Store without Apple’s software — so Apple clearly needs Twitter to give it some visibility on the web, more than Twitter needs Apple.

You can view a demonstration of Twitter’s Ping integration below: