Why Rolling Friction is less than Sliding Friction and is Really Friction not Dependent on the Contact Area?

Answer: Friction arises when two surfaces come in contact with one another with one surface trying to move over the other. In this situation, the irregularity of both the surfaces gets interlocked and the resultant frictional force then opposes the motion of the moving body. 

Friction is dependent on the coefficient of friction (determined by the geometry and type of the surface and amount of interatomic attraction between the surfaces) and the normal force. Rolling friction is less than the sliding friction because of the smaller coefficient of friction as compared to coefficient of sliding friction wherein the surface in contact remains constant.

Yes, it is true that friction is not dependent on the area of contact directly. Friction totally depends on the nature of the surface whether it is rough or smooth. rough surface having higher coefficient of friction hence larger friction force.