I am not too sure on how "empty" the plane should be before the price rises to the next bracket. I was on an EasyJet service, BCN-LTN, last summer. The plane was half full, or half empty, but the price a week away from the flight was around E130 something. I've booked mine two months ahead and got it for some E59.

So, it kinda deters the people who travels on impulse. Something like, "Hey, let's go to the airport and see whether we can get last minute fare to Bangkok. We might be able to have Tom Yam Soup there tonight..." kind of things. They cant just "walk-up" and see whether they can go to BKK for dinner.

If they have a last minute sale thing, whether at an airport counter or online sale, they might be able to sell of the remaining available seats. Hmmm... does this sound like the Lakers Airways/Skytrain thing?