Yes, the addition of "unless absolutely necessary" seems redundant. If one understands the Buddhas teaching on causality and Kamma then one is going to be be careful when making decisions on how to act mindful of the results. The precepts are commonly translated "I undertake the rule of training..." rather than "I vow to obey the commandment..." I'm not sure whether this is because the former is a more accurate translation, or is an interpretation. There have been times I've chosen to break the spirit or the letter of the precepts and I think the most important point of the Buddhas teaching is that I must take full responsibility for those choices and the causal/kammic results. So I think it's primarily about taking personal responsibility, but if in doubt follow the guidelines.
Hi Bodhisvasti, I think this whole thing about the precepts - and especially the one about killing - is just going round and round in circles now, and I really can't see the point in continually arguing about it here, because the precepts are as they are and this is a Buddhist website. You either accept them or you don't, its up to you - and you take the responsibility for that yourself. You might like to have a look at Constitution for Living by P.A. Payutto and at Section 1 - People and Society. 3. The Virtuous Person. http://www.budsir.org/Part2.html#3 with kind wishes Aloka