Added to the convenient reasons you have, Graphic Processors work faster/better with triangles. They can only be in one plane, as opposed to quads. In 3d Art. Artists will work with Quads because those definitely look better than triangles.
It's not just graphics cards, any rasteriser (including software renderers like mine) work ideally with triangles. Although due to clipping, my rasteriser actually works with screen-space convex polys at the lowest level.
And I concur with other posters, pretty neat stuff.
What are you using to communicate with the graphics card? OpenGl? Other? What version of whatever you're using supports the target console? Could you potentially use shaders? I'm concerned about the millions of vertices you mentioned for speed reasons (although as an exercise is just really cool)
At the moment, it's not communicating with a graphics card to do the renders, it's being rendered entirely on the cpu with my own renderer. The planet in the spinning animation is 1.3 million triangles, and it gets renderered, compressed to png and saved to disk in approximately 1 second. I plan to convert it to realtime shortly to let you guys play with making planets yourselves. I have previously used my renderer to render the inside of a box (wow!) in realtime at 50fps using GDI to blit the resulting image to a window.