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.
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.