All manufacturers recommend replacing the brake fluid periodically but almost no one does it until something rusts out and causes a leak or other parts need to be replaced. Brake fluid absorbs moisture from the air through the porous rubber hoses and other seals. That lowers the boiling point leading to one form of brake fade and it promotes corrosion of metal parts.

Power steering fluid normally lasts the life of the car unless Audi has a common problem I'm not aware of. That fluid is hydraulic oil that does not have additives that wear out like in engine coolant or oil.