Does it matter?
"Google's strategy is clear. Play Services has system-level powers, but it's updatable. It's part of the Google apps package, so it's not open source. OEMs are not allowed to modify it, making it completely under Google's control. Play Services basically acts as a shim between the normal apps and the installed Android OS.
"Nearly everything that can be moved out of the main OS has been. The only features left that would require an OS update are things like hardware support, Application Frameworks APIs, and Apps that require a certain level of security or access (like the lock screen, Phone, and Settings apps).
"This is how you beat software fragmentation. When you can update just about anything without having to push out a new Android version, you have fewer and fewer reasons to bother calling up Samsung and begging them to work on a new update. When the new version of Android brings nothing other than low-level future-proofing, users stop caring about the update."