Expansion upgrades and more...
ANet isn’t going to make the expansion available for gems, because it means a 40-60% loss of income for them. Right now, people pay for gems and pay for the game; in the proposed scenario, people would stop paying for the game and just buy gems.
People who can’t afford to upgrade will just have to wait until one of the official retailers offers HoT for a price closer to what they can afford.
WoW uses a different income model and so can choose to afford alternative methods to encourage people to sign up for full subscriptions.
John Smith: “you should kill monsters, because killing monsters is awesome.”