Good point about the static backgrounds, they do look like they could have been preerendred, (although Lasseter is known to be against excessive camera movement for the sake of it) but there is some camera movement at the beginning, that shows that they could move those particle trees if they wanted.
I know the characters are geometrically simple, but what simplicity! Because of the Reyes rendering, there isn?t a single polygon or texel showing.
Today?s hardware is much more specialized and optimised than yesteryears, that coupled with development in tools and shortcuts in the rendering process, I don?t think that a real-time version, of something at least approaching the technical quality of the above movie, would be completely unfeasible on today?s hardware.
But when PS3 with its x1000 power arrives, there is no doubt that it will be. Just look at what is possible on an Athlon 600 in software, with 3½ minutes of rendering:
http://jrman.sourceforge.net/Spacex.png
Anyway I brought the movie up as an example that good image quality is possible even at lower resolutions.