On the other hand... considering they are described as knives with internal reservoirs why exactly would they need to be an exotic weapon? Why couldn't they be handled by throwing weapons? I don't really see any difference between throwing one of these and a knife?
And for the record, just stating the question, someone comes up with a good reason, I'll happily accept it, I just don't see one.
But they are not described as knives with an internal reservoir.
These aerodynamic throwing needles have an internal compressed reservoir with an inertial trigger.
They are basically buffed up medical syringes to be thrown like darts thrown straight on at a target on a fairly flat trajectory.
Most of your thrown weapons tumble in the air as they go, even when throwing knives you have to decide whether to hold by the handle or blade to throw or adjust the spin depending on distance so that you don't thump your opponent with the hilt. (still hurts a little, but not as much nor does it stick

)
So the syringe/darts are a bit different than a lot of the thrown weapons you will commonly use in SR.
It's kind of like shuriken, there are actually different types of shuriken but get lumped under one heading, most classic distinction are the multiblade stars and needle type.
They actually get thrown differently because the star is spinning and cutting while the needle type can be thrown to tumble like the throwing knives for better distance or thrown like dart for a deeper piercing attack but shorter distance.
That said, you would think Thown Weapon skill would cover this as it says it covers a broad range of items, and back in 3rd they mentioned it covered darts.
But they never went into it a lot, kind of like you do not really see spears which I imagine they would probably slap under exotic as well if darts are getting this treatment.
I guess they just assumed most people would stick to knives and grenades.
So I can see both sides of this argument, and ultimately if you want to houserule it under Thrown Weapon it really is not going to break the table.