It is because most people would pass out before getting that wasted. .05 is buzzed, .08 (the old limit) is drunk. I'd be surprised if she could walk at .189
She certainly couldn't drive, which, if you remember, is exactly what happened.
Anyway, you already killed your own argument when you started with "most people". For example, my sister, after a dozen plus pints of McEwans, could easily climb onto a small lounge bar table, cross both her legs behind her head and sing 'The Fog on the Tyne' while others with a lower imbibe couldn't stand up or even remember the words.
I trust you are familiar with the term 'outliers'?