Most of the African immigrants we see today are members of the upper classes- which like members of the upper classes anywhere are going to be well-spoken, easy to educate and palatable to Americans. It’s no more reasonable to compare them to, say, a Guatemalan refugee (who may never have had a chance to go to school at all before now) than it is to compare a kid from the failingest failing public school in the ghetto with a kid from a private school in a rich area.