Of course you have the choice. These are not forced upgrades. It's very simple, do some research, determine if u want it, and upgrade or not. It's 100% up to you.
Yes, it is a forced upgrade. Not right away mind but if there's ever a need to restore then you're forced up to the latest version. I don't know how you can argue that isn't being forced.
I have researched and I haven't upgraded. I'm under no illusion though that I'll always be able to keep the OS version that I want to run however.
That's the beauty of Apples software updates, its available to everyone, regardless of carrier, the day it's released and we all have the CHOICE to upgrade or not. The Android way is to let your cell provider dictate, if and when, you'll even have the opportunity to have a choice. Would u let your internet provider dictate when u can upgrade your computers operating system ? If so, Android is your thing.
I think you're confusing yourself, carrier lock-in is a totally different issue, it's got nothing to do with Android or iOS.