The main reason the US and NATO has been able to avoid heavy losses is as much down to the political work the US states department has done behind the scenes as it is in weapons and tactics innovation by the pentagon. The Taliban and iraqi insurgents has basically had no supply of advanced and heavy weapons beyond what had been available in the country before the wars started. Even much of those weapons were not in working order or secretly bought up by the US or its agents. US and NATO air power has faced almost no real SAM threat beyond a few isolated incidents, which only goes it illustrate how much different things would be if the Taliban had a continuous supply of advanced SAMs and training to use them. Its a similar thing regarding ATGMs, AAA, mortars and pretty much all weapons heavier than an AK47 or RPG. In all previous cases where an insurgent force has been able to deal heavy losses on a technologically superior enemy, the insurgent forces' always had access to relatively modern medium to heavy weapons, and more importantly, a continuous supply of munitions. The technological difference in weapons is simply far too vast for the Taliban to be able to effectively counter the US and NATO forces. Their only really effective weapons of attack has been IEDs and suicide bombs, and suicide bombs are becoming far less dangerous to military forces as training and equipment improves. Take nothing away from the troops fighting on the front line, but things could have been a lot harder for them had the diplomats not done a good job ensuring the really dangerous stuff were kept out of the reach of insurgents.