I used to upgrade my phone once every ~5 years too. Until iOS/Android phones came out things didn't really change much. Sure they got thinner, bigger/colour screens, higher MP cameras, etc. but the functionality was pretty much SMS/MMS, voice calls/mail, photos/videos and that was it. If you were happy with the camera you had and the size of the screen there was very little reason to upgrade beyond fashion.
Now, however, the smart phone I bought last year is struggling to run the latest applications due to it's low CPU speed, if I didn't know how to install my own ROMs (and most people don't) I would be stuck on Android 2.1 and that means I couldn't run a lot of the newer apps. Newer phones have actual useful features being added like HDMI-out, NFC, better battery technology, etc.
Now, however, the smart phone I bought last year is struggling to run the latest applications due to it's low CPU speed, if I didn't know how to install my own ROMs (and most people don't) I would be stuck on Android 2.1 and that means I couldn't run a lot of the newer apps. Newer phones have actual useful features being added like HDMI-out, NFC, better battery technology, etc.