I actually would put more emphasis on teh shades of grey idea, as it is the epitome of human nature. It is difficult to discount the non-human races in ES as being non-human at all, considering that the entire game was in fact designed by humans.
Even the non-human races have human traits, and so each race is meant to personify a different aspect of humanity. This isn't limited to ES, either, you can find it in any fantasy gaem with multiple races.
With this in mind, it opens up teh possibility for any one of the races to be "the good/bad guys". It's a matter of perspective. Let's take another example: the movies The Scorpion King and Teh Mummy Returns. In The Mummy Returns, we see the Scorion King as some sort of malefic monster that, while not being the primary antagonistic force, is certainly not out to save the world. However, in the film The Scorpion King, he is indeed the main character and would be considered the good guy.
You see, it's all a matter of who's stick is bigger (take that anyway you want, it all means the same), and who is the current story's main focus.
For more examples, look into the inevitably terrible sequel to 300 that is in the works, which will have Xerxes as the protagonist.