It is indeed true that all any non-Jew is only required to follow the Laws of Noach as listed by Magdlyn. The trick to this question is that Christians state they are inheritors of the Jewish Covenant (if one makes claim to this, one is essentially making claim to being a Jew in a certain sense, so they may nonetheless be liable for all of Jewish law including the Oral Law in the Talmud, and later Jewish case law and rabinnical edicts.)
Islam itself also states that it has corrected the revelation as given to Moses and Jesus, but much of what they follow is Jewish Biblical law, and their additional rules are essentially as those upon people who take Nazirite vows (like the mother of the prophet Samson, and Samson himself).
Again, without study of the Oral Law, the books of the Bible are useless. Basically, what they tell us is, if you do such and such it is so severe a sin that in God's justice you should have received one type of death penalty or another, but the Oral Law demonstrates that God then showed Moses that God has mercy on his followers (God's followers) and that God never wants such severe sentences to be carried out.
The Canaanites whom Israel was commanded to destroy under the leadership of Joshua were human sacrificers and that is why God's edict against them was so severe. There is ample archeological evidence for this in excavations of the Canaanite Empire of Carthage, and indeed the Romans, while still pagan warred and succeeded against the Carthaginians for this evil of the Canaanites, not just because it was a trade war where the Romans were "cleverer".