1) I'll reveal a terrible secret: most games are made to earn money. And each installment of the Heroes series falls into this category. 2) And this is an official add-on. 3) The appearance of goblins varies from game to game. It may be due to their habitats, or perhaps the developers simply liked to change the design of the green-skinned creatures each time. Or maybe they wanted to show how diverse goblin appearances can be: from monstrous freaks in Heroes of Might and Magic 3 to stately gentlemen with green skin, practically indistinguishable in appearance from humans, in Might and Magic 7. However, they have never been shorter than humans, and in Might and Magic 7, they are even taller. And a goblin knight looks more impressive than its human counterpart. Here are a few examples: here, here, and here.