would it actually be posible to model something like a head or a full character without at least a few tris. Im far from an expert but sometimes when i'm modeling or i look carefully at someone elses wireframe i can at least see a few imperfections. As for a car or something solid i think its easier to get all quads.

I guess though towards animation and tweaking towards the end a reaonably clean mesh would be easier to work with, although i would imagine that even people working with games and animation, that they still find problems with certain things.