[The Saucepan Man]

The 10 Commandments really just tell us how to live together best in a society. Humans, in their early evolutionary stages, came together to live in societies because that was what was best for the survival of the species. And it's not to good for the survival of the society you live in (and therefore the survival of your species) to kill others from the same society, or to cause discord by stealing etc.

Now, I know that the theory of evolution doesn't really fit too well into Middle Earth, but the principle is the same. The various races organised themselves into societies, and therefore developed standards by which to live to make those societies work for the best. So, they didn't really need any Commandments to tell them how to live.