If I remember correctly blender will ask you when drawing such a cilinder how many edges it should have. A higher number means a rounder shape. The problem is that computers can't work with round shapes. So you will always end up with flat surfaces at some zoom level.

But I am by no means a blender expert. I have only used blender to load a model, and convert it to another format.. Maybe they invented some new format that manages to use some kind of vector graphics for 3D models?

No idea, really.