Dann-J.. I agree with the proper weapon focus' adding up but weapon focus in darts, slings and shurikens ? Extra feats might add up on them but they still wont do as much damage as a decent ranged weapon.
Would you in all seriousness, even if you were a hobbit, go on an adventure into a land filled with bandits, trolls and all sorts of nasties with a handful of darts rather than a crossbow ? How far can a hobbit throw ? Certainly not as far as he/she can shoot. Even Frodo the most whimpish one imaginable had a sword.
In D&D halflings are the kings (and queens) of thrown weapons!
Halflings get a +1 bonus to attack with thrown weapons (darts, shuriken, throwing axes, slings), so my halfling party mostly specialises in them for the sake of roleplaying accuracy. The cleric / stormlord throws electrified shurikens (with rapid shot and zen archery). The rogue / shadowdancer flings darts (not for their base damage, but for their sneak attack damage). The ranger / warsling sniper is devastating with his sling (rapid shot, sneak attack, focus, specialisation, improved critical). The only odd-hin-out is the party leader, a tanked fighter / weapon master. He's the party meat shield, holding back enemies so the ranged specialists can do their thing. Although even he has a few stacks of throwing axes.
When you're relying on additional damage like sneak attack or shocking burst, it doesn't really matter what the base damage of the weapon is. And with everyone using rapid shot, even small amounts of base damage start to add up as well. Halflings (and gnomes) also get the benefit of 1.5x strength damage bonus when using a sling without a shield (although not with tiny weapons like darts or shuriken).
In SoZ I've had them take the Missile Volley team feat to make them even more effective. So far they've been tearing through enemies quite nicely - and mostly from a safe distance. They tend to chew through ammo at an alarming rate though. A stack of 50 darts or shuriken doesn't last long with rapid shot active.