I think that a company that thinks like you is quite arrogant. I think that a company should attempt to accomodate all of its clients as best as it can, including previous clients.
You mentioned DVD players in your message. I believe that a BluRay player can read DVDs and CDs. So, your example is not very good.
Finally, I can't figure out how should a calculator application require new hardware.
Apple does accommodate clients as best it can. At some point, however, they have to stop providing updates for earlier hardware; either the hardware just won't support the newer OS or it's no longer fiscally feasible for further updates to be provided. Apple actually tends to support iPods longer than many manufacturers of similar devices do. Your iPod received two major operating system upgrades and many minor ones which brought a number of new features that were not promised when you bought the iPod, and that's all any reasonable person could expect.
That the calculator app you want to buy no longer supports the older version of iOS was a choice made by the app developer. They didn't have to drop support for the earlier version. Paraphrasiing what you said, I can't figure out how a calculator application should require a new version of iOS. There are, however, a number of other RPN calculator apps available and at least some still support early versions of iOS, including one that is free and has gotten good reviews (Free42). Perhaps one of those would suit you.