Glad they're keeping track of this data, puts an end to any debate about whether or not this is really happening. It's clearly a change Apple's made recently, and it definitely impacts a large percentage of older phones.
Apple has clearly discovered an engineering fault with their power supply designs, which was causing phones to crash as batteries aged.
In order to avoid having to replace the batteries of the impacted devices -- many of which are still under warranty or AC+ -- they developed this CPU underclocking code to mask the issue. A hardware-crashing phone by definition is in need of warranty service, but a slow phone is still "working" and so Apple does not have to repair it.
I think we need to make an effort to distance this discussion from the "planned obsolescence" conversation. That is not what is going on, and framing the issue in that context weakens our argument. Apple's misconduct here is in covering up the power delivery fault in their devices, NOT a deliberate attempt to slow down older phones in order to sell upgrades.
It's important to keep the conversation focused on the real nature of this issue if we want any kind of resolution, the most obvious of which is that any device which requires under-clocking to prevent crashing should receive a free battery replacement (if it's under warranty or AC+).
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Just as an aside, I want to note that this issue -- excessive crashing when the battery has lost capacity -- is not unique to iPhones, and has been a common problem in the Android world for as long as I can remember. It's never been made into a big story because, until recently, Android phones generally had user-replaceable batteries.