That's a very good point!
5.56 yaws in flesh like any undeformed (FMJ/ball) spitzer bullet. But it is moving very fast and is very lightly constructed so it fragments after yaw. the fragments open up the edges of the temporary cavity and make it a permanent cavity. Exit wounds up to 6 inches are not unheard of.
Speaking of extremeties, this man was hit with a 5.56 military ball round in the leg. It missed the bone. The bone was shattered and severed into two pieces anyway. I believe it may have been Dr. Fackler that reviewed the story and remarked that this does happen. I've never heard of arms going flying, but I have no doubt that arms are severed from a practical standpoint. I knew a guy that accidentally shot a woman in the pelvis, leg, and knee. It was a complete disaster. No idea if she is alive but I have no doubt she did not fully recover.
Although my military experience is with the M855 round (SS109), I strongly suspect that the move to SS109, 1 in 7 twist rate, and shorter barrels has reduced the effectiveness of the round. Many experts and some lab tests dispute this. But the same people say "fleet yaw" (angle of yaw before impact for a given rifle) dictates the effectiveness or non-effectiveness of the round, yet they dismiss out of hand that a round with a lower twist rate might be more effective.