Android is open, but the Google layer is not. This is why Adblock Plus can offer the app directly to users, but the app is not available in the Google Play Store. The new version of Adblock Plus allows the app to update automatically without going through the Play Store. The update also tweaks the UI a bit to look better in the Holo Theme.This has been a point of confusion around this story, so to be clear:
As before, we would like to mention that you should think carefully before deciding to use an adblocking app. The revenue you keep from Google may be a drop in the bucket, but a lot of smaller developers and content creators depend on ad revenue to offer you quality apps and services. Nothing in this world is truly free.