The concern here is not with murder, but with manslaughter, accidental death. A man who is fighting another, whose wife intervenes and receives a blow from him that kills a foetus, does not intend for the harmless foetus to die. There was economic loss in such cases (potentially, anyway- childbirth was hazardous before modern times), so reparation was necessary. However, if the man used sufficient force to kill the wife, the standard law of lex talionis applied, because it was reckonable as murder.
Hmmm, not sure if I can see your "whose wife intervenes" in the text... and you seem to be claiming that the text only applies if the man deliberately attacks the woman, as opposed to her simply being caught in the melee (caught on the backswing, wayward sligshot, etc)
Can you justify these points?