I don't know the answer to the last 3 sentences, but I can say that there are over a billion Muslims on this planet (as of 2010 the figure was calculated to be 1.6 billion), and many of them are in the same moderate group as many of the Christians on this planet. There are a population of them that are complete nutcases that would gladly blow up women and babies in a suicide bomb to get to some imaginary place though, and the world would really be a better place without them here.
I think it may be fair to say that percentage wise, in the modern world, more Muslims tend to be Koran literalists than Christians who are bible literalists, though there are plenty of both in either religion. Then again, not very long ago in western history, virtually every Christian was a fundie. And therein is the rub.
Western culture has undergone a transformation by way of political liberalism (in the broad historic sense, not the modern sense of liberal v. conservation) and secular humanism. The religions of the west have experienced some degree of transformation as a result. But this is more a case of the religion bending to cultural change than the culture bending to religion.
Most of the Islamic world has undergone no such cultural renaissance as yet. However, there is no reason to believe that Islam is the reason for this. Christians were every bit as backward of Muslims at the inception of this cultural shift we've experienced in the west. For example, in the Christian west they used to execute people for practicing witchcraft just as they still do in parts of the Muslim world such as Saudi Arabia. If "fundamental" differences between the two religions, i.e. differences in their governing texts, are the explanation for modern differences in this sort of behavior, then the Christian west would never have behaved so barbarically, but it did, and for the vast majority of its existence. This tendency to not interpret the Bible literally and to curb some of the most inhumane aspects of Christianity is in fact a very recent development in the west.
Cultural backwardness is the reason why so many people would take a biblical text literally. The OP's fallacy is that he wants to use war like or barbaric passages in the Koran to explain why so many Muslims would take the Koran so literally. Yet there is no relationship between the two. What is actually in a religious text bears little if any relationship to people's tendency to view it literally.
Biblical literalism will tend to diminish as cultural liberalism advances. Warlike and barbaric content in the texts is beside the point. Those portions will simply be seen as metaphorical, or otherwise re-interpreted to be consistent with modern liberal values. When we see some Christians in the west, for example, not believing in a literal hell, believing that non-Christians aren't necessarily damned, or being tolerant of homosexuality, that is an example of religion bending to culture, not a demonstration of Christianity's so-called superiority over another religion.
Culture and religion tend to influence each other in a never-ending causal feedback loop. I maintain that the principle function of religion in society is to justify the existing cultural (and sometimes political) order of things. It tends to put the brakes on change as best it can. It did so in the west for hundreds of years with its selective opposition to science and to equality based on gender, sexual preference, and sometimes race. Indeed, it continues in its attempt to put the brakes on these changes. As it does in the Muslim world.
The Muslim world is simply on a different cultural timeline, probably 100-200 years behind the west in many respects. A higher degree of textual literalism in religious belief is just a symptom of that. In the longrun, however, the contents of the texts matter very little. They mean whatever the practitioners of the religion want them to mean.