So, what's to say the other half accidents were caused by inebriation? Accidents happen and people get killed all the time. I don't think it is safe to assume that someone with a .08 limit gets in an accident and kills someone that the alcohol was necessarily to blame.
You have to be really careful with tests like this. They are worded to make a case and a point but that point may not be the actual cause of the issue.
Okay, sure, it's possible that none of the other 40 whatever percent of 'alcohol related' traffic deaths were totally unrelated to the alcohol. For that matter there is no reason to think that the ones with >.15 BAC were in any way affected by the alcohol. However there is VERY strong evidence that being inebriated interferes with ones ability to operate machinery safely. and my point stands I think that people do ge tkilled because someone with a .05 or .06 or some stupid kid with a .03 for that matter did something they might well have not done if they were fully in control of there faculties.