This should be required reading for all logo design clientele out there. Summed up, it basically says that your logo doesn't have to literally interpret what your company does. For example, Apple Computers (well, now just Apple): there is nary a computer-related item in this logo. Yet everybody knows they make computers.
The article is best summed up in this sentence: "... what you include in the design of a logo can be just as important as what you leave out."