i dont think the US is as wicked as you think. THey have nothing to gain by decimating the Pak armyUS is looking for an excuse to decimate Pakistan's military and Kayani has resisted the bait.
When fighting a superpower, the worst thing you can do is to fight head on. There are always alternative ways to engage someone at their weaker points (supply routes, insurgency, etc.). For a change, Pakistan is defending itself using brains, not brawn. Against America, Pakistan's brawn is negligible.