Let it be known that I barely understand what setuid/setgid/whatever is. I think it has something to do with what user a program is executed as. This brings me to
In Security Enhancements in Android 4.3, Google says
The /system partition is now mounted nosuid for zygote-spawned processes, preventing Android applications from executing setuid programs.
It makes no sense to me to say that a filesystem in Linux is mounted "for" anything, as if the way it is mounted can be relative to a process or executable. If the system partition on Android devices is mounted with
nosuid, then how can any of the system's core executables run as root, which they need to do in the earliest stages of startup?