I'm thinking its an artifact of who won, the Christains won Rome, and by consequence, Europe. Rome fell and Europe beat the tar out of itself for several hundred years but they did sit on decent geography, Gaul e.g. being a pretty choice piece of real estate. Perhaps the physically broken up nature of Europe (mountains, islands, forests, penninsulas) allowed for a more 'Risk' game of constant competition and indepdendent languages, but no matter how you slice it, Europe went on to colonize the world, have strong armies and navies (good real estate helps these things).
Islam sprouted up in the 7th century and while successful, never accumulated the technolgy and wealth of Christain Europe when the rubber hit the road (industrial revolution).
People that have all the stuff gravitate towards law, order, and secular principles (as far as I can see, pretty much anywhere).
If Martel had lost and the Moors conquered and re-settled Europe, forgotten about northen africa and the middle east over the centuries only to return as the owner of everythig to drill oil a millenia later I think it is perfectly likely that the region could be dominated by disgruntled chrsitains and/or jews cutting hands off.
Barbarism seems barbaric when one has lots of cool stuff, water, food, medicine, and HVAC. People showing up with dictators and toys seem blasphemous to the disenfranchized.
Or, alternatively, Islam more represents a reverision to the more militaristic old testement meme's as opposed to all the fuzzy Jesus stuff, which is rather confusing to me given that Islam embraces Jesus, allegedly.