Ouch. This was some marketing gone very badly. Although in the last few years Apple products have gotten less user serviceable. Even the new Mac Mini now has RAM soldered to the motherboard! I'm typing this on a Late 2012 Mac Mini which originally came with 8 GB of RAM but I upgraded to 16. The old non-retina MacBook Pro (still available) has some user serviceable parts but the Retina models are more locked down. This is the really sad thing; Apple can, and used to, do better
I don't see anything wrong with using an older computer. Sure, newer software often expects newer hardware and things might go slower than usual, but I don't think that warrants a full computer upgrade every year (and if you ask me, software developers are to blame). I'm personally using a 7 year old desktop; I've changed the motherboard and added more RAM, but that's it. I do have a newer laptop, but it's much nicer to type on a mechanical keyboard and look at a 24" screen.