It's a tricky matter really. I get the consumer angle but there is a technical angle. A new system is a new system, and it likely has new chips. It's only fairly recently we've seen consoles stick with effectively the same commoditised chipset from generation to generation with the XBox and PS being effectively PCs, but before that there's been a lot more divergence in architecture. Now if the hardware is significantly different that requires emulation. Software emulation however requires the host machine to be significantly more powerful than the target. The alternative is hardware emulation, ie having chips on board that can do the same job as the predecessor's chipset, but that adds significantly to the build cost, and likely causes compromises with design, battery life, heat, etc.
Now if Nintendo are going with a bump like the one from DS to 3DS then yeah backwards compatibility is probably doable, as there's enough similarity between the systems - let's imagine it's still NVIDIA hardware but they've just taken a new more powerful variant off the shelf. However, if it's a shift to fundamentally different hardware, or indeed a fundamentally different form factor, then backwards compatibility becomes tricky with the former requiring emulation and the latter maybe rendering it impossible (ie if system X uses 2 screens and system Y uses 1 you end up with a horrible mess of 2 screens squished onto 1 as happens when emulating DS games on a PC - just as an example).
Now assuming backwards compatibility isn't offered and companies port their products to the new system, there is a cost to those companies in doing that. Sure not the same cost as initially designing the game, but a cost nonetheless. If they're using something like Unity or Unreal Engine then likely there'll be a pipeline to export from the base project and while that's still some work because they still have to figure out optimisation (ie how many polygons can we display in this scene) and figure out any control scheme changes between systems and so on. If it's a custom engine, they need to build a new version of the engine and port to that. All of this is work and gamers moan at having to pay for work that someone did, as if they're entitled forever to have that work free after buying one thing they did.
I'm pro-consumer, I shop on GOG, I admire Nintendo's choice to go with honest up-front cost instead of microtransactions, I buy physical so I have the option to sell my games 2nd hand if I so choose. I'm not a corporate boot-licker. I am however a programmer, and so I see the issues with this.
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