Like you said torture is clearly defined. The only people argueing that the common definitions of torture is to strict, are the ones who wish to use torture. Even if it may only just be a bit, and for good reason.

Even if you have no plans on killing someone, if you abuse them to the point where they think you will kill them, that is torture. If you yell at someone and say, "Tell us what you know or we will kill you!" That might be a grey area. If you stick a gun into their mouth and yell, "Tell us what you know or we will kill you!" That is torture, even if the gun is not loaded and you have no plans on killing them.