Why are most runways laid out in a generally East-West direction?
While there are many exceptions to east-west runways, generally speaking prevailing winds (which blow from a single direction) blow east-west rather than north-south. It happens because of Earth's rotation generates Coriolis effect. 



There are other wind patterns besides prevailing winds. Trade winds occur near the equator and flow from either the north or south towards the equator. They curve towards the west due to the spin of the Earth. Polar easterlies blow close to the north and south poles. They blow away from the poles and curve east to west.

Hence, most of the runways are Eastish-Westish (not exactly East-West).