That's the whole point of those demos. It wouldn't be impressive if it was just an animation 
Maybe not, but even if it was I enjoy the music and art & firework a demo is.
More and more often I find my self just looking at demos on YouTube.
Is I'm NG users, it does make sense to run in on OS4, fake AGA modes are slow and does support 320x200 only 640x480, and can't run any of demos in EUAE, because EUAE PowerPC jit is limited to 68020.
anyway its not so impressive run the demo that was designed for 50Mhz on 1800Mhz, its bit silly :-D, anyway who cares, there is YouTube.