Well, I am a bit confused. Griffiths himself writes in his book "Introduction to Electrodynamics" at one point in his book that this law is "simply wrong". In a footnote, he writes that it was wrong in principle wheras it is true for non-relativistic speeds, and later on in his book, he goes on to prove that. (Example 10.4) What my confusion is that this "true for non-relativistic speeds" is also true for Coulomb's law. Why isn't that law also "simply wrong" then ?