http://www.onemanga.com/Naruto/230/04/
I always thought because of this, right after he attained the third pupil. That's why Naruto had to prove it to him that he in fact could scratch it. But for some reason, I always thought it was accepted by the community because of something I read way back when that Naruto was defeated by Sasuke because Rasengan lost to the Chidori. Which I didn't believe or accept... But I suppose brighter minds have prevailed this time around.