The Guild Wars Facebook Page has more on the microtransaction system in Guild Wars 2, following up on the recent update on the ArenaNet Blog on the business model for the upcoming MMORPG sequel. Here's word:

Here are a few important clarifications about our microtransaction system. First, that gold is coming from other players. So somebody must have an abundance of gold if he trades it to a player. The system is not adding new gold from the outside.

Second, take into account the gem/gold trading system. Everything that is in the store will basically be available for gold with this system - so it doesn't really matter what is in the store, as it is also available for players who play and don't want to spend additional money. Hope that helps! ~RB2