http://www.uesp.net/wiki/Oblivion:Armor
http://www.uesp.net/wiki/Morrowind:Base_Armor
http://www.uesp.net/wiki/Skyrim:Armor
Memory usage, each type of armor needs a different lightmap, transform matrice per body area thereby causing each combination of armor pieces to occupy an oufit slot and thereby using more memory which reduces available memory for greater quantities of NPC's unless they are similarly dressed (the memory usage tends to increase exponantially - reducing the number of variables/body areas typically reduces the rate of memory usage increase, ex. reducing the number of NPC races would have even greater affect because they are the Base but doing that would basically impair the Lore/story/style of the TES world signicificantly - Creatures and custom races aren't generally a factor as they rarely spawn in variety - usually multiples of the same type which is much easier on memory usage than NPC's)



In England we also say Kekks and Trou, but we don't claim that its an evolution of the English language, its just slang, where in retrospect, You calling trousers pants could be seen as slang and not correct.