There are some exceptions to this: the Ten Commandments are known by heart, as is also the Quran: it is known by heart like the poem.
There is no exception to this. The Ten Commandments are make sense rules attributed to God and it could still be all boiled down to the Golden Rule, because some of those Commandments are things that should be obvious.
The Quran is not known by heart unless you read/believe in it.
Moreover, the Quran was not revealed as a written book: it is the Recital of Gabriel to Prophet Mohammed.. then when it was written, it is then was called a book.
In the end, it is still a book, written by a man. Regardless of how it came to be, it is a book man-made and used for Power and Rule over other men. It is no different than the Bible in that case, nor is it any different in how it is used/translated.
In the end, the books are used for Power and for the Powerful to hold dominion over other Men.
Moreover, God promised to keep the Quran from human manipulation, because it is the last heavenly book to be the argument against the disbelievers among people till Doomsday,
God may promise but that does not mean MAN promised. The moment words are written, they can be manipulated no matter how much promising is made. All it takes is one man who sees Power through the words and it is done.
To not admit such is to know nothing about men or humanity at all.
As to whether it's the last heavenly book; why? Why should it be the last? Because a prophet of God said so? But that is only the belief of a select few; others believe the NT of the Bible is the last holy words... or what if someone in the future comes up with more Words of God... why should not their book be the last heavenly words?
Thus the fallacy of man - thinking that they know with absolute certainty how God will interact with the world.