The Koran is very chaotic, inconsistent and contradictory compared to the Bible. It was slap dash thrown together. It is written in "religious Arabic" thus open to even more interpretation.
The Muddled Message of the Koran
http://www.prophetofdoom.net/quotes.html
The Bible has plenty of chaos and contradiction too, depending on how you look at it -- and who does the looking. (See The Dark Bible, for instance.) And even leaving aside such obviously prejudiced and hostile commentators, all religions have various sects with often contradictory interpretations. There are probably more variations within Christianity than within Islam.
But that isn't really the question, is it? The article doesn't discuss internal contradictions within Islam or within the Koran -- it talks about how contemporary Islam differs from the historical record. My point is that Christianity has evolved just as Islam has, and perhaps more so. I just don't see why that matters to anyone other than "true believers".