that's probably because those are Highpoly models, which is what you use as a base to make the textures
(depending on what method you use to make them, I think, just a 3D artist so I dunno for sure)
Usually high poly are used to bake normals (and AO maps) onto lower poly models, giving the illusions of much higher poly count therefore making the model look more detailed. You simply just would not UV something that complex (or it would take days

). Depending on the 3d artist and who he's working with in tandem for the textures (unless he does it himself

) a low poly will be done first then UV unwrapped, then the low poly is built upon adding details then it's baked on to the low poly to give Ambient occlusion and normal maps
Just as an example
THIS is a single plane comprised of
two Polygons baked out from an object that comprised of tens of
thousands of polygons and using a 3x 1024 texture map (diff/normal/specular maps). A decent hi-poly mesh can make a low poly count model look absolutely fabulous, along with a decent set of texture maps you can do fabulous things and low poly costs.