Apple has traditionally disabled some features when sending out a new iOS update to models that are one or two-years old. Despite this, some users have complained that Apple is using planned obsolescence to force those with an older iPhone to shell out the cash to buy the newest model. A class action lawsuit was filed against Apple last month, claiming that Apple misled with its statement that iOS 9 would be compatible with the Apple iPhone 4s.
The plaintiffs included Apple marketing documents in their filing, which stated that iOS 9 was faster, smoother, and more responsive than iOS 8. Not only were these statements not true in their experience, the suit claims that Apple had to know about the drop off in performance.
Up until iOS 9.2.1, iPhone 4s users had found no improvement in their user experience with iOS 9. But the latest build of Apple's mobile OS seems to have turned things around and could be a sign from Apple that older devices will be treated more kindly with future iOS updates.
source: iAppleBytes via AppleInsider