That's funny, cause the height, shape and general designs of buildings in TF2 arn't exactly realistic either. IE they are warped for the art style.
Despite the fact that i did geology at A-level and am used to studying rock formations (such an interesting life i live), i could see this in TF2 with only a reasonable amount of suspension of disbelief on my part.
Plus, from a gameplay persective, you don't want to confuse players with what is and is not a walkable surface. Rocks on a 45 degree angle of descent is one way to achieve this confusion. So some shape modifications on Rexy's part are completely understandable.
Considering A) direct affect on gameplay, B) general map size and relative prop size, and C) general aesthetics vs performance, my only complaint is that the tops appear too square.
EDIT: Oh, and it makes me want to eat some of these: