That table is misleading as it only lists the smallest bomb you can use to destroy the object. The hardness could be 10lb, but since we don't have a 10lb bomb, it would list the 100lb bomb as "hardness."
It's further confused by the fact that our bombs don't do the "listed" amount of damage. As you get larger in bomb weight, the damage-to-weight ratio gets wider. The 100lb bomb does close to 100lbs of damage, but the 1,000lb bomb does something like 850-900, IIRC.
