[scarface74]

And it couldn't be they reduce performance to keep the phone from shutting down prematurely when you have a bad battery- a known issue that people were having?

If they wanted to encourage people to buy new phones wouldn't it just be easier to not support older phones with new iOS updates? Why base the slow down on battery life instead of just slowing the phone down after two years?

There are much easier ways to encourage people to buy new phones if they wanted to be underhanded than the Rube Goldberg conspiracy that you are suggesting.