It's not due to exploiting, it's a smart move on them to prevent server overload.
As posted on Gameinformer:
"In order to help alleviate some of the server strain currently affecting Guild Wars 2, NCSoft is suspending digital sales of the MMO directly from its website.
You can still purchase Guild Wars 2, but you will have to head to a retail location and pick up a copy of the game in a box. NCSoft makes the most profit from sales of Guild Wars 2 from the digital versions on its website, so the company is, in essence, taking a financial hit in order to make the experience better for current users better. When you head to buy.guildwars2.com, you are greeted by a "sold out" message on all the available skus.
Star Wars: The Old Republic pulled a similar move by limiting sales when the game released last year."
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