Yes, displacement maps are a lot more render intensive, but normal maps don't ACTUALLY alter the geometry. For instance if you look at the silhouette of your normal mapped model, there will still be edges. - normal maps still have the same basic idea of normal bump maps in how they only affect the lighting during the render process - so it still has the problem where the more parallel you view your surface the less of the normal map detailing will be seen. That's the way I see it anyway...