Brake fluid is significantly different from power steering fluid and other types of automotive fluids. Power steering fluid is petroleum-based, while brake fluid is alcohol-based. Introducing a petroleum-based fluid into a car's brake system can result in severe damage to the rubber components of the brake line.
Brake systems that operate on alcohol-based fluids have a number of advantages. Alcohol absorbs any moisture that gets into the brake system and is resistant to temperature extremes and other elements that can potentially damage the brake system. If power steering fluid is accidentally or intentionally added to the brake system, the only way to reverse the damage is to disassemble and thoroughly clean the system and then replace all rubber parts.