I don't have a clue if Professor Gates was arrested primarily because he was black. But I can certainly say that it is not just blacks who are arrested every day for what is being called "comptempt of cop." Police officers have developped a theory, which is not backed up by any actual written law, that they are the dictators of the immediate area that they occupy, and that citizens owe them absolute obedience to their commands and complete deference to their majesty, or else risk arrest. While blacks may fall victim to such arrests at a higher rate, this is not just an issue of racism. It is an issue of abuse of power as well.
Update: Carlos Miller has many of the same thoughts, and a lot more detail. Having been arrested himself for "comtempt of cop," he should know.