Additionally, dividing the airdrop in 5 stages is a clever decision in order to maintain followers interest during all the ico. Usually on most Airdrops people just fill in the form and forgets about the underlying project.
Not only that but with the requirement of posting at least 2x per week is a good way to keep it on the first page too, attracting more and more people and you can't forget it does help build a lot of thread pages quickly.