It seems to me that the three Petrelli sons are being developed into a very neat set:
Gabriel's power is mind intensive. Peter's power is empathic. Nathan is strong-willed, and Arthur pointed out that in ep9. My question is....with this nice set, could Nathan possibly have a yet unmanifested power related to his will? It just makes sense. After Peter got Gabriel's power I knew that Gabriel would get Peter's. I wasn't sure how it would happen, but I was right. When Sylar said Claire was special, I knew it meant more than just the fact that she could regenerate, and I was right then too. I'm not saying my speculation will be 100% accurate, but there does seem to be a strong inclination toward triplism in the Petrelli bros. Plus, it would explain why Nathan appeared to have no power before the Company gave him his flight ability (Peter and Gabriel's powers also couldn't be measured conventionally). Also, the writers have Heroes have explicitly stated that Arthur does not have the hunger. It seems that he has already overcome it...which means he had to have it before. How does that play into everything else? Is the hunger perhaps something related to but independent of Gabriel's power? Or has Arthur had Gabriel's power before? More and more questions keep popping into my mind.