I'd assume the solution was introduced with the iPhone 6. The problem was there much earlier, due to the way Li-Po batteries work.

As such, it could even be counted as one of the touches Apple is known for that other OEMs don't bother with. It just needed better communication.

Can confirm. My 5s suffered the random shutdown issue and wasn't part of the throttling fix.

Yes, this was a feature. This feature was so great that they kept it a secret and were subject to lawsuits and forced to pay millions in fines.

They were fined for not telling people about the feature. The feature still exists.

They introduced in direct response to people keeping their phones for longer--an more recent industry trend that has been well documented.

You seem pretty certain about their intent. The truth is Apple added battery throttling in iPhone 6 and up not in their older phones even though their older devices were capable of CPU throttling as well. For example, the iPhone 5S would throttle if it got hot enough to protect itself, yet it didn't receive the same throttling feature for the battery.

https://arstechnica.com/gadgets/2013/10/ipad-airs-a7-chip-is...