Uthman did very big favor to truth by burning the copies that had been circulated world over.Why?Because when Islam got established the teaching started and students were coming from non Arabic speaking areas and learning Islam and they were writing Quran verses or hadith(sayings of prophet)or different aspects of Justice on same paper,or leather sheet,then going back and sometimes these writings got messed up due to rain or other natural factors and people could have been confused.Then some Muslims were writing in their accent.,eg.you say Joseph and Yousaf,both right but yousaf better,you write ottoman but in arabic we say uthman,in urdu we say usman.This could have lead people to confusion.So it was a very great work what uthman did.May ALlah reward him for this.But don't forget that there were the pople who were sitting in the committee compiling Quran were from the time of prophet Muhammad and there was total agreement in both the contents of Quran and language.No dispute not even for a dot or coma.The period between Muhammad and Uthman was short well observed and there was no disagreement among any of the members of committee.If this would not have been done then imagine today we would have been seeing problem.Today you go to any country and buy Quran in arabic and bring it and match it with others you will not find a differentce of even a dot or coma.Thank you Uthman for this.