Hey, DarkOne,
I'm sure that Glenn would tell you that the ticket sales are due to a combination of two major factors.
The first reason would be the exclusive sets, the likes of which haven't been seen since ProgPower VI. Personally, I feel that the higher card of Stratovarius, Seventh Wonder, Jon Oliva's Pain, and Pain Of Salvation is right up there with the legendary higher card of ProgPower III. Mind you, I know that Blind Guardian, Angra, and Gamma Ray had a greater drawing power just based on their status and exclusivity at the time, the fact that three of next year's acts are playing some classic albums makes this a more even match. Though next year's higher card will certainly bring people to the fest, I think the ticket sales are that much greater due to the fact that everyone knows what they're getting with these sets.
Second, it stands to reason that when folks are aware that they may never have another chance to experience something, be it a product that is available to purchase or an annual event, they tend to get their asses off the fence. For instance, when Hostess briefly went out of business, people searched far and wide for what may have been their last boxes of Twinkies and Ding Dongs. Likewise, when progressive and power metal fans hear that the festival made with them in mind may only be around for one final shindig, they suddenly have the money and time to attend. Cinderella put it best with their biggest hit: you don't know what you got 'till it's gone.
Stay metal. Never rust.
Albert