It should be noted that my understanding about the development tools that Apple offers will prevent third-party is from compiling apps that support older platforms after a certain point.

However your original point stands, and not only is the iPod touch fourth-generation five years old but even when it came out brand new it was less capable than the iPhone apple sold at the time.

Someone who had been continuously using the device would not have really been screwed because that person but already have the apps he or she needs to use, there would just be a day when the app versions would stop updating. Yes if you ever delete those apps you will probably not be able to install them again because those old versions aren't offered anymore.

Obsolescence can really suck, but at the same time nobody should use devices incapable of running a patched and current OS on the Internet. The only difference between an iPod touch 4th gen and a computer designed for Windows XP is that the computer is capable of running a current, patched lightweight Linux distribution and the phone isn't.

Perhaps someday phones and mobile devices will realize this same capability future, but until device drivers get less proprietary I don't see it happening.

Note that OP's iPod touch is still perfectly capable of playing music and videos.