As far as I understand it, the point isn't just to pressurize the propellant to get it out of the tank and into the engine, but to maintain pressure so that the propellant remains liquid.
If the pressure in the tank drops, the propellant would turn into gas which would effectively be lost and potentially dangerous (by allowing flames to go the wrong way).
As your link points out, helium is nice because it is inert and remains a gas even at liquid hydrogen temperatures.
If the pressure in the tank drops, the propellant would turn into gas which would effectively be lost and potentially dangerous (by allowing flames to go the wrong way).
As your link points out, helium is nice because it is inert and remains a gas even at liquid hydrogen temperatures.