After reading some of the claims listed on the site you linked to, I can conclude that there is an element of misinformation behind the content. And because there is so much of it, it would be unfair to expect me to sift through the material and provide a rebuttal for each claim. So I will direct you to a book which, if you sincerely desire the truth, should answer your question: http://islamicbookstore.com/b7626.html
If the Qur'an has never been altered, what about all the claims that it has listed here: http://www.answering-islam.org/Quran/Text/
The Muslim Perspective
Why does the Messiah have to come twice? Couldn't Allah have two different souls to accomplish the missions of delivering the Gospel and be the End Times Messiah? Was he short of supply?
By what criteria do you attribute veracity to your faith's sacred text(s,) and thus the basis of that faith? Is that criteria objective?
Why is there religion?
How does your particular faith conceive of vegetarianism and why?
Answers: Atheist, Christian
What's the most attractive thing about your worldview? What sets it apart from the others?
Muslim Islam vs. Islamism: The Dilemma of the Muslim World Asghar Ali Engineer Muslim Islam Fazlur Rahman Muslim On Developing Theology of Peace in Islam Asghar Ali Engineer Muslim The Rights of Women in Islam Asghar Ali Engineer Muslim Islam: Misgivings and History Asghar Ali Engineer Muslim Islam in Contemporary World Asghar Ali Engineer Muslim The Prophet of Non-Violence: Spirit of Peace, Compassion & Universality in Islam Asghar Ali Engineer Muslim Islam: Religion, History, and Civilization Seyyed Hossein Nasr