Forgive the intrusion from the non-RPG
world, but I find this a fascinating topic, and can't resist the urge to propose a conceptual framework
One important distinction might be between prejudice and other forms of racism. By prejudice I mean, literally, pre-judging a person, based on first impressions, typically because it is expedient. For example, you are walking alone down the street and see a group of tough looking strangers that appear to be of a different class or race than you, walking towards you. You decide to cross the street or otherwise avoid a confrontation. Lets be honest, people of all races probably do this more often that we're willing to admit. It is arguably an acceptable form of prejudice, because in a potential survival situation, you are making a rational judgment based on limited information as to the best way to handle the encounter. It would be surprising (and quite irrational) if this same behavior didn't manifest itself in most RPG "encounters". After all, the death is the rule in RPG much more than in real life, so this would tend to increase the survival benefit of prejudice.
Other forms of racism might be defined as judgments (whether before or after you know the individual) based on ignorance or hatred, rather than expediency. The important difference is that these types of racism are irrational. I leave it to the reader to fill in their least favorite example.
The interesting question is, how much RPG racism is based on expediency, and how much is based on these other factors? Ignorance may not be an important factor, because all players presumably have perfect knowledge of the documented characteristics of each race. I suppose its possible players might decide to role-play their character's ignorance, but I don't get the sense from the write-up that this happens very much. The remaining basis for irrational racism in RPG's is antipathy or outright hatred. In some cases, hatred between the races is a documented feature of the game milieu; failure to be racist would in general be out of character in these cases. Here, racism is an artifact of the game rules and not necessarily an example of real world racism intruding into the game.
But, its possible (and likely, judging by the write-up above) that some game characters engage in (non-expedient) racism in the game merely because distaste for certain game races has become part of the player culture, even when the game or scenario rules don't explicitly call for it. Here would be a true case of real world tendencies towards racism migrating into the game.
RPG racism vs. real world racism -- I think there's at least a good term paper in it!