The system works fairly transparently: Chronoscrolls can be purchased for real-world cash and then placed on the auction block, and a scroll thus purchased can be redeemed for extra subscription time. That means that players with piles of in-game gold can get plenty of free time to play the game. And if you're wondering why you'd like to spend that money, there is an event taking place starting on Friday, June 29th, in which players will hunt down reptilian egg thieves for special rewards. So you've got some motivation.
[Thanks to Dengar for the tips!]