Or simply not that great normal maps.
Take a look at Crysis's parallax occlusion mapping. It's amazing. An otherwise flat surface looks real.
http://wiki.polycount.com/ParallaxMap?action=AttachFile&do=get&target=crysis_parallax_occlusion_mapping.jpg
http://windows7themes.net/wp-content/gallery/crysis-texture-mod-parallax-occlusion-mapping/9.jpg
http://img16.imageshack.us/img16/9669/crysistexturemod.jpg
Visually, Skyrim would benefit heaps of things like this, because a lot of Skyrim has rocks and stone-walls/floors and such.
Nothing that a Qarl/Bomret's Texture Pack for Skyrim doesn't solve, in any case...^^