Yet, this doesn't seem to be a real problem. That's because it just doesn't happen this way, despite some passing mention on a page trying to make a point.
If this were really the problem it's made out to be, the solution would be mandated. Think about it: if this really happened, there would be a LOT of cases of people just driving along in hills/mountains, crashing because their braked suddenly didn't work. Yet, we hear no reports of this, no lawsuits for suddenly inoperative brakes, no outcry for a solution to "save the children." Why? Because it just doesn't happen that way. The heat builds up *slowly*; there's a reason for that. The pads themselves are made of material that doesn't transfer heat well at all. The calipers act has heat sinks. The fluid is one of the LAST places the heat goes, by design. Because of this, the fluid heats slowly; it doesn't just all of a sudden flash into steam. When it does form steam, that very act takes a lot of heat energy, which tends to cool the fluid. When this happens, it limits the amount of gas in the fluid, which means the driver will (should) notice the pedal getting spongy or soft. This is (should be) a warning to the driver. Of course, with the brakes getting this hot, there will be a definite odor of burning brakes by this time; another warning. As well, the brakes will start to fade, again giving the driver more warning.
Do people ignore these warnings? You bet they do. That doesn't mean the brakes are at fault. It doesn't even mean water in the fluid is at fault. It's driver error. The driver is responsible for the safe operation of the vehicle.