I have to question both of these statements. The typical 3 to 3-1/2 inch diameter “ninja throwing star” with six to eight points has an effective blade length of less than two inches; worse yet, the geometry of the star ensures that the adjacent tips will come in contact with the body and stop the leading tip from penetrating even to its full depth. Another problem is momentum; a properly overhand thrown knife enters the target tip slightly up, digging forward with its rotational momentum contributing of the long arm contributing the maximum mass to penetration. This can be seen in the fact that longer blades of the same weight will penetrate deeper (although they take more skill to throw correctly). A throwing star has no long axis; with the mass disturbed symmetrically about the center of mass, it provides a lot less effective penetration force because of the lower angular momentum per unit mass. This, combined with the typically small mass of throwing stars limits their penetration ability. It should be noted that actual shuriken were derived from trowels, awls, needles, and other nominal implements and tools, and were never intended as primary killing weapons, but rather devices to distract or temporarily disable an opponent while making a primary attack. “Ninja throwing stars” became popularized because of the spate of ninja-themed movies in the late 'Seventies and early 'Eighties, and also because throwing this type of “weapon” into soft pine or styrofoam is much easier to master than a thrown knife or heavy dart.
As for the injuries to the neck and head, the jugular vein and carotid artery are nowhere near as vulnerable as most people believe. The bulk of the vessels are protected by a thick mass of muscles including the sternocleidomastoid. Anyone who has butchered an animal can testify to how difficult it is to cut through that muscle in a single blow even with the leverage provided by a fixed blade cleaning knife. The actual area that the vessels are superficially exposed is roughly the area of a quarter and is just below the jawline, so it is far more likely that a vertically thrown star would run into the jaw rather than penetrate the neck. The forward temporal region of the skull is quite thin and it is possible that a thrown star could penetrate, but again it is a small region (about the area of a half dollar) surrounded by much thicker bone, and even a full penetration is no assurance of death; the number of people who have survived shooting themselves through the temple (sometimes with little or no actual functional impairment) is legend. A strike to the back of the neck at the base below the occipital may be more incapacitating, but again, there is a lot of muscle there, and below the occipital region of the skull the spinal cord is pretty well protected by the spinal column; you’d need to be very lucky to go between the bones.
So, you’d have to be very, very lucky to kill someone with a “ninja throwing star”, and even a thrown knife or traditional shuriken is far from assured. A tomahawk, on the other hand, has enough momentum to penetrate deeply and with training can be thrown with good enough precision and force to cut into the chest cavity, penetrating a lung, which will slow anyone down.
I can penetrate watermelon skin with my fingernail, and punch straight though one with a closed fist. (I’ve seen people penetrate through the skin with an index finger strike but I’ve never conditioned my hands to withstand that kind of force.) Shooting, stabbing, and otherwise mutilating fruits and vegetables is a visually impressive trick but it is nothing doing damage through the surprising strength and resilience of human epidermis, fascia, and muscular tissue.