This is only because Islam has not had their reformation yet, although there are movements in that direction. "Salvation" is possible in Islam (although they don't call it that), but the primary difference is that in Islam, good works are taken into account as well as faith, whereas in Christianity only faith is required. I have read both the Bible and the Quran, although my Muslim guide told me that reading the English translation is not really as accurate as reading the original Classical Arabic. To be fair, he admitted that there is the same contention in the Muslim world, with some Muslims believing that Allah and Yaweh are the same deity and some vehemently stating the two gods are incompatible. He and I had very interesting debates. There were actually four of us - Muslim, Christian, Jew, and atheist. We all got along and respected each other, and we frequently commented that if we could do that, there is zero excuse for others to not do so as well.
All that being said, I honestly believe that this question can be debated, but it cannot be truly answered. We can't exactly ask the authors of either book for clarification on the matter.