Why do Hill and Frost Giants have a bigger damage bonus than their Strength bonus?

Question

In the D&D 3.5 Monster Manual, a Hill Giant's damage entry shows:

Greatclub +16 melee (2d8+10)

A Hill Giant's strength bonus is +7. Since there doesn't appear to be any magic abilities or feats that increase the bonus to damage, where does the additional +3 damage come from?

The Frost Giant has the same problem. Their damage entry shows:

Greataxe +18/+13 melee (3d6+13/×3)

However, their strength modifier is only +9.

Answer 1

The hill giant and frost giant are both using two-handed weapons (a greatclub and a greataxe, respectively), and a two-handed weapon gets a ×1½ STR bonus for damage. With fractions rounded down, +7 × 1½ is +10, and +9 × 1½ is +13. That's all that's going on.