It actually varies from school to school...like she said some don't start interviewing until very late while others do early, which would probably increase the % of seats filled in first wave.
I think the "you're done for" mentality regarding not getting first wave invites stems from a number of things.
-The knowledge that you have to continue to stress throughout the next year
-Wanting to plan for the next year but having to wait until acceptance/rejection
-Early acceptance means I can withdraw any other apps and save money on interviews!
Honestly, I think it goes hand in hand with thinking applying late is the end of the world.