So yes, this story is pretty much an excuse to show off our fancy new Android story category (it's 2014. We thought it was time), but hey, it's still informative.
In case you've been wondering why you don't see many applications with Google's new Material Design just yet, it's because applications created with the Android L Preview SDK may not yet be submitted to the Google Play Store. In fact, said applications won't even run on non-Preview devices to begin with.
Alongside the release of the Android L Developer Preview images, Google also released the Android L Preview SDK. Using the L Preview SDK, developers are now able to make use of Theme.Material.* and give their applications this highly sought after theme. And in fact, this is only available when using the preview SDK. However, Google makes it very clear that applications created with the preview SDK should not be published to the Google Play Store.
It's pretty clear Material Design simply isn't done yet, and as such, Google has wisely decided to not let developers use it in the real world just yet.