MMORPGs as a whole are designed to spread content through the level range, where equipment is relatively scaled to what you need at the time. In WoW, you can easily survive till level 50 by just using the loot that you find on enemies you defeat. If you stick with the quests that are given, you get great level specific hand outs. Unfortunately, once through in the existence of a higher level, players will not care about the content that they are already in.
It is this style of player that is prayed upon by the Gold/gear sellers. They want to experience the high end of a game, and don't care at all about the low end. They do no care about the quality of the level 10 quests, or anything else that doesn't gratify them instantly. No matter what a game developer does, they will never be able to prevent this manner of thinking without abolishing the entire working model of an MMORPG.
People love progress. They love the thrill of leveling up and gaining near gear. Gold Farming is just an byproduct of the system.