Powered Equal. hub centric, MAGNUM Tire Balancing Compound, EZ Balance, Centramatic dynamic wheel balancers, etc. are all accepted different methods of balancing tires. The Powder that you are probably being told about is "Equal balance powder".
I am not a big fan of any of the balance systems that amount to something just being dumped into the tire and then letting gravitational pull move it into points of balance.
Now to try an help answer your question; ALL TIRES regardless of what they are on should be CORRECTLY rotated and balanced for best life and wear of the tire.
Now the method used is becoming some what controversial with all the new systems that being developed.
Use what ever method you are most comfortable with. Below is a couple of links to the Michelin and Good Year tire web sites, they offer there own theories on this.
I am old school and still shave balance the tires on our track cars(only thing that I find acceptable at speeds in excess of 150 mhp "I'm trying to teach the grandson how to win races from my years of experience from the school of hard knocks").http://www.michelinrvtires.com/michelinrvtires/hom_us.jsphttp://www.goodyear.com/rv/