Do you think the gas meter on your car lies? You know the one - it tells you there are 10 miles to empty. I am guessing it's "conservative" which is a kind way to sayinaccurate.
I think this because I don't believe the car makers want me to run out of gas so they intentionally pad the measurements in case I decide to push the envelope.
I think this is what they do because we do exactly the same thing on power warnings.
When you look at the percentage available warning on a Power Plant, we've padded it slightly so you'll not hit the wall and crash. Our wattage measurements are entirely accurate but our cautionary systems are "conservative".
I think it's a good thing that manufacturers pad their warnings so consumers can push the envelope just a little.
If you see me with a gas can along the side of the road, you'll know I was wrong.