All built-in plugins are included in the Gradle project, it does not need to download the plugins when using.
But one still needs to download custom plugins. Before gradle-debian-helper, packages in Debian also needs to specify the local Maven repo URL. I think it would be a bad idea to integrate the Android plugin into Gradle itself, because it is just not part of Gradle. Maybe we can have something like gradle-debian-helper but for Android applications? A.k.a, "android-debian-helper"?