Isn't this just the perceived difference in source? i.e. mocking someone for what you believe is a positive character trait is generally seen as okay (the aforementioned "study a lot"). Another vein this happens in is with regards to Germans ("being precise").
I don't think you could say that there's a similar vein of humor with African-American culture that's developed, and that's principally historical: America's slave holding history is still an open-wound today, and its social concepts around African-Americans were widely based on making sure they were viewed as lesser.
EDIT: This isn't to say either is ultimately good. There's a pretty important difference between occasional good humor that transitions into something of more malevolent intent, but how people perceive them appropriateness very much matters.
I don't think you could say that there's a similar vein of humor with African-American culture that's developed, and that's principally historical: America's slave holding history is still an open-wound today, and its social concepts around African-Americans were widely based on making sure they were viewed as lesser.
EDIT: This isn't to say either is ultimately good. There's a pretty important difference between occasional good humor that transitions into something of more malevolent intent, but how people perceive them appropriateness very much matters.