with as many rounds as they're shooting on a daily basis and with as many 203's that they unload, a couple shots into a car would do little to dent our taxes. the IEDs thing seems plausible.
when i first saw the video i thought of Full Spectrum Warrior. during training they tell you to save your ammo and use your grenades wisely because you're given a limited supply during combat. funny how i thought of a video game first. anyway, if they're unloading like that, and as quiet as it seems there, i'm sure ammo isn't far away, nore is backup if they need it, but that's just my deduction.