Some things are so horrible that they don't deserve an apology, and surely what Materazzi said to Zinedine Zidane in the world cup final was one of those things. It has nothing to do with fair play - Zinedine Zidane got and accepted his punishment for what he did. Materazzi got all the glory in the world and his apparent apology is not credible.
Zidane has apologised to his fans and to the football world, and we have accepted his apology. That he does not want to apologize to Materazzi should not bother anyone.
Zinedine Zidane will always be remembered foremost for being one of the greatest players ever, and a man of honour. Materazzi is the complete opposite.