This is why ray tracer demos love showing off spheres made of millions of polygons and so on. It is cheap to do. However turns out polygons aren't the only thing that matters for graphics.
The spheres would most likely be represented as an equation, not a soup of polygons. It's much more efficient (not to mention a whole lot easier) to raytrace. It's also infinitely precise, which is actually why a lot of people are more interested in raytracing than approximating things with polygons.
For instance, it's a heck of a lot easier to render isosurfaces in a raytracer than turning them into a big polygon soup and rasterizing that.
... low amount of apps, etc.
You can install Debian packages on an N900. It's essentially a tiny ARM tablet running Linux.
What the large print giveth, the small print taketh away.