The article rightly makes the point that they have huge forces and zero staying power. Give them a week and their logistics will be on the verge of collapse. Even the Iraqis did better then that the first time around.
Another point: they have an incredible amount of infantry, but their armored strength is less then impressive (the most recent tank given in their list is the T-62; 115mm gun but unimpressive muzzle velocity, armor's hopeless against modern munitions). Men against fire. As any soldier or commander from World War I onward can tell you, fire kills. Not men. They've got a lot of targets, but all that's going to get is some gunner on an LAV or Bradley painting huge numbers of hash marks on his turret.
The only viable threat North Korea really has handy is the fact they could make South Korea uninhabitable for the next few decades via chemical weapons alone.