It's a huge problem if I tell a computer to do something and it doesn't do it, it does it half way, or it usually does it but sometimes doesn't. We engineers need to have a Hippocratic Oath that starts with: 1. Never put the company's need over the user's intent.
And, yes, I understand disk caches and why we have a graceful shutdown process. What irks me is that the computer might be in the middle of doing something despite my not having told it to be doing anything.
It could easily and even possibly be fairly argued that there's a massive difference between updating 3rd party apps and updating the operating system itself.
The Play services were originally an immutable part of the core OS, but it meant that security updates relied on the manufacturer to push updates, which were useless useless at doing.
I am minded that everyone would laugh at me if I took an un-patched Windows XP system on the internet, yet using ancient Android 4 is still common place. A PC can function offline where as most people can't isolate a phone (from multiple networks) without loosing the core functionality. The PC can be blank; phones usually contain all sorts of personal and private information.
Personally I want OS's to leave me the hell alone, but actually, I can't really blame them for trying to protect their users.
Updates to the OS come as OTA notifications that I can choose how and when to apply (download+install separately, for example). I don't monitor my Play Services version, but I assume that it's silently updating in the background, unlike either my apps or the OS itself.