Why do some Christians ignore the 10 Commandments?

If you look at the normally accepted ten commandments, there are more than ten. Different religions group them differently so that they can fit into the idea of ten but this means that in some religions "Thou shalt not kill" is the fifth commandment while in others it is the sixth. If they are both claiming ten commandments but can't decide on how they are numbered, it means there must be more than ten. If you look at them carefully, you can get thirteen.