Anyway, lighting (which includes shadows, of course) is very heavy stuff if you’re making use of todays possibilities like Ambient Occlusion (AO), Variable Penumbra Shadows (PCSS) and Global Illumination (GI) in a fully dynamic way. At least to me that’s one of the biggest improvements over earlier games .It makes everything look much more convincing than the comparatively flat and simple lighting that we had in the DX9 days.
And that’s just one of the many things devs have at their disposal. There are others, like all kinds of physics (water, smoke, …) which had either been faked in the past or didn’t actually allow you to have an impact on them. So if you want to be “wow”-ed by how the game looks, you need some beefy components. On the other hand, if you don’t want any of that “mischief”, it’s not that easy for devs to bring a full-blown graphics powerhouse of a game down to old hardware and still look good-ish. If your whole lighting is dynamic, you can’t simply flick a switch to use image-based shadows for older hardware. That would take a lot more effort.
Basically, there are always new techniques to do everything (old and new) more precisely (less glitches) that cost even more power, so no end in sight.
So everyone needs to decide for themselves how important visuals are to them. For me, once I’ve seen something done better, it’s hard to go back. That’s why I’m always frustrated, if a new game doesn’t support stuff like AO, for example.