Yellow is the new Green...

So if the national threat level is never going to go below "Yellow" (elevated) - which is the lowest it has ever gone since the system was instituted, and where we are now - what's the point of having Blue (guarded) and Green (low)? Isn't that just a 3-level system, instead of 5-level, which gives you less wiggle-room in trying to convey different levels of threat, which was the whole point of the system to begin with?