[salmanarshad321]

Maybe because while reading you're not required to open your mouth and physically speak. That's just my reasoning. Islamic rulings are based on the Qur'an and the Traditions of the Prophet (pbuh). There are about a million traditions on a variety of topics. The scholars keep them in mind while giving a ruling. So, I'm in no position to give a ruling on this. A Google search on the topic tells you that it's not, but none of the answers are satisfying for me so I think I'll have to visit a scholar and ask him/her.