Unfortunately, this is a sad but regular scenario now. It doesn't matter whether Apple does it on purpose or simply doesn't care, but new versions of iOS degrade the performance of older devices (an in this case "older" doesn't necessarily mean "very old"). Some people simply choose not to upgrade, but this may have security implications - and in any case sooner or later you'll come across an app you need that doesn't work on an older version of iOS. You will upgrade, the performace will be degraded, and your previously "good enough" device will suddenly feel sluggish and old.
Is there any definitive evidence for this? Has anyone benchmarked devices before and after upgrades to prove it?
Edit: I don't mean CPU benchmarking which has been discussed elsewhere in this thread. More like usability testing, sequences of actions not invoking new OS features where possible, and also a second set of tests using new OS features because that's what most people's experience would be.
It's difficult to achieve because one cannot downgrade a device to some older version. So when 3GS became insanely slow with updates, no one could at random get a device with an old OS version.
