[jeshin]

What they're getting at is that while it is the amount of amperage that goes through your heart that determines your likelihood of dying, you need a certain voltage to overcome the resistance of your skin to achieve such an amperage. Anything under around 50v is generally safe to touch, and often high amperage applications are under that limit.

So the reason high voltage is more dangerous, if it has sufficient amperage backing it up, is that the higher the voltage, the better its ability to pierce your skins resistance and flow through your body to begin with.