That's not accurate.
Yes, AppleCare+ is an extended warranty, but it also covers things from the date of purchase the warranty does not:
AppleCare+ for iPhone extends your coverage to two years from the original purchase date of your iPhone and a
dds up to two incidents of accidental damage coverage, each subject to a service fee of $29 for screen damage, or $99 for any other damage, plus applicable tax. In addition, you’ll get 24/7 priority access to Apple experts via chat or phone.
So without AppleCare+, as an example you won't get a shattered screen replaced for $29.
Allowing customers to "pre-upgrade" is what they very successfully did with the iPhone 8; I pre-authorized my upgrade and then was able to complete the order immediately when orders went live.