That is terrible to hear what happened to your brother.
Living in NB, Canada, black ice, ice and snow etc are daily driving issues from mid October until late April.
The poster mentioned lifting his foot off the gas. Thats a common mistake in most vehicles. Some automatics have a coast feature and they can get away with it but the engine braking and even drive train drag in rear wheel drives is enough to lock your tires up.
On a straight away you can drive 50 mph + on black ice or glare ice without trouble as long as you know you need to be careful. Once you get going too fast, the force of trying to drive the car against the wind resistance will spin the tires and you will lose traction. 4wd's can go quite a bit faster as the force is spread to the front wheels too.
Big risks of this include coming up on someone going slow, and side gusts of wind. Studded tires and soft compound tires help. Soft A/S's as good as snow's when on ice. Cheap hard snows and mud tires on trucks are terrible.
Normally you'd never go this fast because of turns. As the previous poster said, you have very little traction so a patch you coasted over on a straight away will put you right in the ditch on a turn.
Your tires only have so much traction so you can use it to turn or accel/decel. If you come into an icy turn too fast, you only have one hope, that is to not accel, decel only as fast as wind resistance and make the most smooth and gradual turn the road permits.
Sometimes you get lucky and the ice is either under or over the snow outside the wheel tracks. Depending on speed, you grab a little of this with your tires as it has more traction. If you are going too fast and the snow is deep+semi soft, and you take too much of the side snow, it will grab the front tires and cause massive oversteer, or you will just loose all steering and head straight to the ditch. If it is frozen ruts you will get shoved sideways back towards the centre of the ruts.
Anyways, just a bit of the fun we have everyday.
BTW, up here the biggest black ice problems are:
1) Skim of wet snow packed onto cold road by traffic.
2) Rain onto way sub-freezing road.
The freezing rain causing black ice isn't so much an issue because everyone can see it on their car.