Affording 18 Str, 16 Con, and the other stuff is kinda hard.
As for making sure they're dead, they live in a world where people can be six seconds from death, and some guy says some stuff about divine assistance and he gets up like it never even happened. Also, the whole evil savage dick thing. Not to mention all those enemies that wasted a feat on Cleave have to do something with it, right? Sure Orcs don't have it, but others do.
And if the first attack misses, well the second likely hits. AC 15 means 1/4 chance they both miss, otherwise at least one hits.
Remember also this is happening in every round, in every fight. So even if the first time only the second one hits, or they both miss, your luck will not hold out, and you will be the next victim of Iterative Probability.