A revision is a sweeping change to the basic plan of government that amounts to a rewrite of the constitution by altering the structure, powers and responsibilities of the three branches of government. An amendment is a more limited change that improves the way government works or carries out better an already existing intent. Based on that distinction, Prop. 8 is an amendment.
"Show me just what Mohammed brought that was new, and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached." - Manuel II Palelologus