Why does the US military R&D seem so slow to adjust to the battlefield situation in Iraq and Afghanistan?

If the British had been as slow when the Nazis were at their doorstep, they would most certainly have been overrun. Why haven't they implemented the IDF's anti-RPG system yet on their vehicles? Why haven't they fielded IED-resistant vehicles on the battlefield yet -- you know, vehicles armored more at the bottom and sides and with hulls shaped like a boat? Why haven't they supplied servicemen, both US and Iraqi, with bullets incorporating pig's blood and fat -- to at least demoralize the jihadists who are mostly impressionable anyway? That's what Gen. Pershing did when there was a Moro rebellion in the southern Philippines during his tenure there!!