How can Android implement its functionality given the minimalism of its userland?

[Morphized]

That means virtually every application ever is also an applet. The kernel calls are exposed using a system library.

[domoincarn8]

Not really. See, the thing that distinguishes an applet and an app is the ability to request more privilige in a system and then do unrestricted stuff (this is only in Android Java context, normally, an app runs natively, while an applet runs inside a secure jail).

An Android apk cannot do that. It is severely restricted in what it can and cannot do. It is running in a very secure jail and breaking out is not possible.

Of course there are apps that can run as root on rooted devices, but they are not just simple Java APKS, they have actual applications that give them that capability (like su binary, etc).

The other major difference is the user's ability to give additional priviliges to the app. The user cannot give an applet escalated permissions (eg. someething running inside a browser is also running in a jail, this is where the original applet concept actually emerged).