Can't stand this mentality. Sometimes there are features that are needed that aren't available in the previous OS. Sometimes developers force us to upgrade because some of our most used apps only support the latest OS. There are a lot of reasons why people upgrade. Apple doesn't force anyone to do anything, but they are notorious for planned obsolesce and purposely include new features that aren't available in older OS's ... or drop hardware entirely.
You left out folks who had some issue that required a restore. Apple then FORCES you to upgrade then as well. Well unless you want to just look at your broken iDevice and not use it. IMO the restore option in iTunes should restore the installed version so when there is a problem you can fix it and stay where you are. And the upgrade/update button gets you the latest version if you want it. Never happen but would certainly make since esp for users with older devices that are not yet ready to throw their devices away yet.