Maybe it's just me but I find this whole process to be silly. Why can't the conductors be required to be THHN/THWN-2 and marked on the conductor like it is when I buy a spool of wire. From everything I've heard I would guess that dual rated (THHN/THWN-2) wire is more readily available and cheaper to manufacture than a plain old 90? conductor. So when needed one can strip a piece of NM and use the conductors individually. Even though this isn't permitted I'm guessing that it's a very common installation practice.
Yes, how many of us have stripped a piece of NM just to get a short length of wire for a short connection or jumper for an install?