Wow, as I read through this post I had so much to say!
First, I was a PC guy for many many years...I was one of those people building PC's in the 80's...and 90's...and 2000's. I switched to apple for two reasons...first I was working away from home for a few years and the original iPhone was the first to offer a real browser and a similar experience to a PC when I was not he road...the second thing that stopped me building computers and buying Macs was my audio system. I had carefully built a small server to stream music to my system...after spending a fortune and picking each component, a friend brought over a base Mac mini that costs $600 and sounding much better. My main rig is still a dual boot win10/hackintosh macOS 10.13...but whatever issues I have with Apple...they make great computers with great software that poses far fewer problems for the user...If you can afford it...and care to...I believe its a better solution than anything else...And...this coming from a hardcore computer guy who always swore I'd never go this route.
But...
I do think they should have explained what they're doing. It does cause distrust. But, I don't think they did it to force people to upgrade...
When you can't load new software on your old hardware...there are reasons. Software has basic requirements in order to work properly...over time(and this has always been the situation with computers and used to be much worse), hardware specs change and many machines can't support new functionality. Think...bluetooth 1.0, 2.0, 3.0 or PCIE 1.0, 2.0 or USB 1.0, 2.0, 3.0...these changes need to happen for computers to progress and for the functionality that we all use and appreciate every day. A five year old computer usually has 2 gigs of ram...that's a joke. you can't even run a modern operating system properly on a machine like that. Often the limitations imposed are for your own good. If you have a computer for 7, 8 or 9 years old...you can't be upset you can't access modern software and features...move on. For decades I had to build a new machine every year to have modern functionality...it's not like that anymore and getting much better all the time.
And Shadowfax...a motorola flip phone...thanks for the levity

)) but, we're talking about incredibly powerful pocket computers...not phones. but, if you tested it...you get a fraction of the original talk time you did when it was new...
And Ultrafast69...I've never noticed a router or any computer that plugs in slow down. If I did, I've found slow downs are due to software getting corrupt or bogging due to poorly executed uninstalls. Most computers benefit from a fresh operating install every few years. Even today...endless updates isn't the way to go. Internet providers can probably be blamed more often for internet speeds...but your router does have a processor in it...it does throttle down when not being used. I recently cleaned the vents on the bottom of my apple router and found it clogged with dust, and it was running hot, so I'm sure it was throttling. Also, hard drives and partitions can get messed up and slow things down.
As far as iPhone or iPad speed...and I don't know anything you don't...
Usually a modern processor throttles down all the time when it's not working hard. If you go purchase a new intel 4000mhz processor...it doesn't run 4000mhz all the time. It will very often at idle or while your doing basic functions, run at 600, 1200, 1800 MHz...whatever is needed to complete the task quickly...what does quickly mean? Who knows? whatever intel deems necessary. When you decide to RIP music or video that same processor may run at 4200 or 4400 or even 4600mhz! speed you didn't even really pay for. The max is based on a number of factors but the most predominent are heat, temp, needs, motherboard, firmware, software, # of cores running...on and on...that same processor may also run one core...or six cores...mostly based on how the software was written. On PC's that are plugged in, this came about for energy efficiency, almost exclusively.
Your phone is the same way, I don't think they ever run full speed, they would get very hot and kill the battery in hours. As batteries wear out...and they do...phone life decreases dramatically. Batteries can lose 10% per year of their capacity...especially things like phones that we rarely charge in a manor best for the battery...my phone gets plugged in when it needs to or when it's convenient for me. So, I think there logic is, when your phone reports it's battery state is degrading to apple (and it does) instead of a max of 1000mhz, and four hours of battery life...they give us 80% processor and six hours of battery. I'm not saying that's there formula, but the logic. The answer, replace your battery every two or three years...if it bothers you. I just upgrade my phone every couple of years and never notice a thing.
The point I was trying to make...this is not to get people to upgrade...it's about user experience and energy efficiency. This is a common practice in the industry...across all companies and all devices. It all comes down to batteries and energy storage...and they aren't that good now. Much better then when we were kids...but still have a long way to go. Batteries and energy are the key to everything in our tech saturated world. But, We all want to be green...