Seeing that 80%+ of iOS users update to the latest OS within the first 3 months according to Apple’s charts, why would you think that if Android users could update they wouldn’t?
Yes, if users get a notification that says "hit this button to update" they'll do it. The question is whether they see that as a substantive benefit. I would predict that most users don't care, just like most don't care about filesystem access or sideloading.
I'd say this is one of the things Apple has been very successful at. Releasing a new version of iOS has become a highly anticipated event for a staggeringly large portion of the user base. From the way they handle updates on a software level (auto-updates and persistent notifications) and on a social level (turning it into a large PR event tied to their new generation of devices). It's something Google was never able to do, and I don't think it's any accident that Android updates are lagging so badly.
I think there'd be a veritable shitstorm if, say, AT&T suddenly decided to withhold iOS 13 for 6-12 months, while it's effectively SOP for Android devices (where you have manufacturers needing months to release a new version, then providers who delay it even further to test ... something).
iOS is very annoying about updating. It's much less work to update than to constantly ignore warnings. High adoption rates therefore don't invalidate OPs point.
I hate that iOS downloads the updates in the background and uses up data quotas without warning and without consent from the user. The only solution to prevent inadvertently updating is to go to the storage settings and delete the downloaded update, only to have it get downloaded automatically again in a matter of days or weeks.
Low Data Mode in iOS 13 should make this stop (although they don't say it on the support page, it shouldn't do it if they are blocking App Store/iCloud updates...)
https://mixpanel.com/trends/#report/ios_13