The final products of those amazing programs that show up late in the platform's lifetime are indeed running on the same hardware, but aren't those programs often developed using faster computers of later periods?
For instance, Donkey Kong Country does run on an unmodified SNES purchased on its launch day, but its creation shouldn't have been possible were it not for the Silicon Graphics workstations used to create the art, which was most likely vastly faster than the development hardware used to create the earliest SNES games. Many amazing pieces of code involve pre-rendering or other various forms of precomputation that are extremely computationally expensive but the final result will run on a low-powered machine.
What we're seeing on the BBC Micro, MegaDrive/Genesis or other evergreen demo platforms is not "what would happen if computers never got any faster," rather it's more like "what would happen if only the computer running the final product never got any faster." We still need faster, better hardware.
For instance, Donkey Kong Country does run on an unmodified SNES purchased on its launch day, but its creation shouldn't have been possible were it not for the Silicon Graphics workstations used to create the art, which was most likely vastly faster than the development hardware used to create the earliest SNES games. Many amazing pieces of code involve pre-rendering or other various forms of precomputation that are extremely computationally expensive but the final result will run on a low-powered machine.
What we're seeing on the BBC Micro, MegaDrive/Genesis or other evergreen demo platforms is not "what would happen if computers never got any faster," rather it's more like "what would happen if only the computer running the final product never got any faster." We still need faster, better hardware.