Unless you want, say, security updates. You're also forced to buy a new phone/device if you want them after x years too, where x is a low number
But I agree that anyone buying a new phone is stuck with iOS 6.
Also, while the 3GS (June 09) is getting ios6, the original ipad (April 2010) is not. Apple will abandon their equipment just as fast if it suits them.
Indeed. I am quite frustrated that my first-gen iPad is, for whatever reason(s), not deemed worthy enough of iOS 6.