I would say that both types of warfare are nothing new. The 20th Century mechanized the "conventional" style of two hordes running pellmell towards each other to hack away, but the process of refinement began a couple of millenia ago when the Romans added the innovation of forming the horde up into neat lines. Perhaps its most accurate to say that the 20th focused so narrowly on refining that conventional style that armies were caught by surprise by the reemergence of asymmetric warfare in the second half of the century. What we're seeing now is, perhaps, rectification of that mistake.

I agree wholeheartedly that mechnised warfare wins no hearts and minds. Its apogee, raining down wholesale death and destruction from 30,000 feet with cold impersonality, can only terrify and destroy, but it cannot convert. I think what I find hopeful in Petraeus's doctrine is that he advocates warfare on a retail rather than wholesale basis, and that it again matters that the soldier has a face. That soldier may begin by breaking down the door and shouting orders, but once he's inside the home, there's at least a chance to make some civilized connection. No chance of that if all you do is blow up the home.