OK let me phrase it differently with a group of questions. So, is there a limited supply of gems, or is the supply unlimited? Say I were to go out and buy 50000 gems from the gem store with my VISA card (~60000 gold) where do those gems come from? Could I get hit with a message saying there are not enough gems? What about the gems you get in achievement chests? Where do they come from? OK, so call me a skeptic, but I don’t believe our illustrious currency exchange is entirely untampered with. Are gems becoming more expensive or is there so much gold that it’s becoming worth less? What happens if the demand for gems to gold conversion exceeds the amount of available gold coming in (XMas maybe?)? Will ANet deny the transaction or will they just generate more gold? NSF?
ANet will gladly sell you as many gems as you care to buy. Remember, when you buy them, you’re not telling Anet what you plan to do with them. So, you could be planning to buy store stuff for yourself or others as well as convert them to gold.
How does this relate to the exchange? If there were ever a situation where the amount of gems players put into the system increased a lot, the gold to gems rate would go down so that the orders are generally covered by the gold put in. Of course, this would also mean that the gems to gold rate would also go down, so the market would likely correct as people decide to hold onto the gems until they get a better rate.
Since what we see is generally the opposite, this would be the result of there being more gold going in than gems. Fwiw, people who have a lot of gold might also want to give gems for Christmas — without spending IRL cash. Also, while some people are cautious about gold, more people are going to be cautious with RL money, as running out because of profligate gem buys might have negative consequences people prefer to avoid — like eating only Ramen for a month.
Gold can be accumulated with time in game. The cap on gold accrual is time available, as well as the earning potential of the game modes one prefers. These caps can be exceeded with more time, a change of play style or simply being patient to accumulate. RL money has to be earned somehow, and for many people the cap is not something as easily overcome. Finally, MMO’s are a game genre that is built around the idea of players sinking large blocks of time into the game over lengthy time periods. This favors gold accumulation, making it more likely that there will usually be more gold going into the exchange than gems.