Maybe Nathan WAS indeed born with abilities, but his father hugged him and they were gone afterward. Then he got the injection and everything was well again.
The only reasonable explanation to this could be that Nathan has a power like Sylar. Sylar's power was never detected by any markers (they thought he was a Telekinetic). Seeing how powers develop later in life he could be a missing link.
Btw, it's a shame that Mr. Petrelli's power is only working when he touches someone. If not, his telepathic powers wouldn't even have to be his. If his powers worked a little bit diffrent, it could be that Maury was using his power to comunicate with Arthur, being affraid of Arthur.
This would make my theory have more scence in the way that Arthur is just collecting a bunch of people to get their powers. Which results in collecting Matt, solely for this powers, so Maury didn't have to give them to Arthur.
I would love to see how Tracy, Nathan and Matt kick Arthur's ass. In my opinion they make a nice team. I like Tracy (esspecially after she mislead Mohinder in touching her). Nathan was always a smarter character and Matt is just so cudely friendly.
In my opinion it's a shame Peter allways had the save the world. He's pretty stupid, falls for every trick and doesn't seem to notice how stupid he is in every damn situation. It's much like Goku and Naruto, which I also hate, because they act so damn stupid, but because they are so powerfull it doesn't matter.
I'm getting more respect for Claire, because she actually acts more smart as time flows on, she's really growing with her powers. The last episode is a good example for this. I would love to see her walk in with a bombbelth to get rid of some people.
Intelligence > power, in my opinion. I would rather see a smart person use his seemingly useless powers than a dumb person always get away with his mistakes, because he's so damn powerfull.
Only Hiro, in my opinion can act a bit stupid, he's a funny character and doesn't really seem dumb, only a bit childish. Peter however has a bunch of cool powers and allways seem to use them in a wrong way.