Don't forget that Termis often take a Storm Shield or two which provides a 3+ inv save against the AP1/2 heavy weapons. As jams has indicated, the higher the number of shots the higher the likelihood of rolling ones (or ones & twos with the 3+ inv on the AP1/2 shots)! Unless your opponent's luck with the dice is like mine than the Termis simply get wasted with simple bolter shots!!!The key to killing terminators is just pure weight of fire. Yes it's nice to have ap2+ guns but they're generally rare and/or expensive and therefore quite difficult to pack into a list in sufficient enough numbers.