This has nothing to do with RETRO or NOSTALGIA. The demoscene happens today and every production is made and thought today, and doens't want to "relive old memories".
With this in mind, it's not apples and oranges ay all. Both C64 and ZX Spectrum have a bigger, more active, more prolific scene producing demos, games and tools, without a hint of nostalgia at sight. The Amiga is a computer of the same category (old), and there's a shitload of stuff to do with it, and probably a lot of limitations to break, but hardly anyone does it.
If you don't see the zealots, you haven't kept up with "Amiga" news for the past 10 years