[jrockway]

I was told the travel websites buy seats in block and resell them

If anything, this is technically wrong, as airlines don't sell "seats", they sell tickets. You don't have a guaranteed seat until your butt is in one and the door is closed.

But as the blog mentioned, perhaps the airlines have decided that overbooking is going to make them look bad during this event, so they are only selling inventory for available seats. Unusual, but it makes sense.