Yesterday they were having a "woot-off", where they replace the item with another one as soon as it is sold. This happens infrequently, randomly, and lasts 24-72 hours, depending on what they feel like doing. What you see today is the way Woot works the rest of the time. One item per day. When it's sold out, they don't replace it until tomorrow.
Sorry, just saw that the pp told you while I was posting!