Except they're really not different. Just because Android runs a distinct userspace and windowing system doesn't make its Linux kernel any less Linux. You can easily install a Busybox userspace on a rooted Android device, and on top of that you can start building an entire GNU/Linux userspace, complete with package managers and X server. Install a VNC viewer in Android, and you can even connect to your local X server and have a fullscreen X session.