I actually think that the presence of traditional symbols of evil is a better way of handling good and evil than it might initially seem, as to play on the preconceptions of the player to cloud their judgment is a very realistic theme. We live in a very "enlightened" time in which stereotypes and prejudgment are frowned upon, and free reign of these are only really allowed to play in entertainment and fantasy. Warcraft uses the fantasy dynamic of portraying primitive, traditionally evil races in combat with advanced, traditionally good races in order to recreate the theme of civilization against savages, one that has historically been a very serious one.
Even with the founding of the United States, and even in the south, where slavery was most concentrated, it was universally understood that slavery was, in abstract, a bad thing. It was excused by stereotypes of Africans and their descendants as simple, stupid, savage people who were only happy when controlled by others and would resort to truly monstrous and animalistic behavior if let free. In modern America we've mostly erased all mention of the old extremely crude and brutal stereotypes used to justify slavery, and hidden the memories away in libraries and academics so effectively that today many younger people would never recognize the old stereotypes.
Throughout history, endless wars and evil acts perpetrated by societies have been justified by widely-held beliefs in the inherent savagery and evil of certain other peoples, thus justifying brutality revisited upon the monsters. To have good and evil in action be more shades of gray and subjective opinion is very unusual; even the fierce debates of modern politics are rarely matters of full-on good and evil, and even then they are the few isolated conflicts that rise to the top of debate amongst thousands of less prominent disagreements or judgments that everyone can agree on. In most cases, disagreement about good and evil is a matter of disagreement about facts, and very often this is a matter of what preconceptions and stereotypes those committing evil have about the victims or their actions. Even the holocaust was ostensibly justified by portraying the victims as evil and the perpetrators as upright and noble protectors of humanity.
The Knights of the Old Republic games utilize this to apply a sheen of gray to the dark side, but they are fundamentally limited by the fact that the underlying world asserts that the dark side is evil, so for them, any indications that it's merely misunderstood are red herrings, and the player knows it. Blizzard (the company that owns the Warcraft universe) is free cut out the evil at the core of the Horde stereotypes, and leave only your preconceptions behind, thus recreating the good and evil debate in the form that has plagued humanity throughout history. Indeed, it's this very form of good against evil that dominates many discussions on both sides involving Al Qaeda, the West, Islam.
[ October 16, 2007: Message edited by: Jonathan S. Fox ]