Yeah - but that's specifically a subheading under grappling, so is that unarmed damage or adjusted unarmed damage for putting the hurt on someone you've already grabbed?
Nobody is quite sure, but the current hypothesis / likeliest explanation is:
1) the book was supposed to say somewhere that base unarmed melee damage is (Str/2)S
2) this was left out or lost in an edit
3) there's an orphaned reference to it under the grappling rules
I think all you can do for now is use (Str/2)S. Note that this interacts quite weirdly with melee weapons though, which all have fixed damage codes that do not take Strength into account. A lot of melee combat builds will do more damage with their fists than with any melee weapon.
It is also possible that (Str/2) was intended as special rules for grappling damage and that normal unarmed damage has a fixed damage code. We just don't know right now.