Fralex
Explorer
Just different. They are not finesse, light, two-handed etc. You can't be disarmed. You can't use it for unarmed attack nor sneak attack.
It seems needlessly complex to create an entirely new class of weapon that only applies to one thing. Couldn't they have just given it the Special quality and briefly explained in a footnote that Unarmed Strike is a natural weapon, not a regular weapon, and is different from them in the following ways?