The iOS downgrade prevention mechanism also forces you to upgrade to the latest version, even if you do not want to do so willingly, if you ever need to restore (reload) the OS on your device. If iOS gets corrupted somehow and you need to reinstall, the only version you are authorized to install is the latest version for your particular device.
Even if I had not gone to the slaughter willingly, if the OS had ever spazzed out on me and required a reinstall, I'd have still been screwed. You aren't allowed to reinstall the exact same version that's already on the phone if what you have on it isn't the latest version.
So if I trade phones with someone, I still run the risk that at some point, I'm going to be forced to upgrade.