It even happens with big-time mmorpg's like ultima online, too, for that matter. Just search it up on ebay, "ultima online account". (I saw people selling rare UO items for as much as $30 - $81, and what's sadder, people actually bidding on these items!) It's very sad, and not the right way to make money at all! I'm glad this game doesn't have that sort of thing.
I won't get into the debate on whether it's _right_ to buy online game cash or items for real cash, but here is the reason why I did it once, back in Everquest.
There was an item I really wanted, really really wanted. It was a major upgrade in my equipment, was one of the best pieces of equipment for my class and had such a great special ability it made my character much better. I played a Shaman, was able to heal myself or others reasonably well, was able to regenerate mana better than any other class in the game but all my damage spells were either very inefficient or were DoT (Damage over Time) so multiple castings of the same spell didn't increase the damage immediately, instead it just lengthened the duration of the DoT.
What I wanted, and why.
There was an item often referred to as the 'Space Ghost Blaster' - a wrist item that you clicked on and did 270+ damage, took 8 seconds to cast. Using that item I could click on the blaster (ok, so it really was a JBB, Jaundiced Bone Bracer), blast for damage, heal myself (healing all damage I took during that 8 seconds), click on the blaster, and be far more efficient than trying to heal / blast / regen mana.
The problem with obtaining the item.
It was a rare drop off a rare spawn. The spawn was in the back of a dungeon that required a balanced group to progress to it (at least at the time) and behind a locked door so you had to have a rogue with you to be able to get to the spawn location. If you ever screwed up and died back there you would have to get another rogue to come in, unlock the door and let you get back to your body.
Once you did manage to get back there, a single character was able to solo that room. The spawn location spawned something every 20 minutes, it had a spawn table with several different possible monsters, you were hunting one specific spawn, so on average it would take 2-3 hours before the right mob even spawned. One he spawned, he had several items he could drop, the Space Ghost Blaster was just one of them. On average you could expect to kill him 4-5 times before the item would drop.
What does all that mean? Time. It took a very large investment in time to have a chance of even getting the item. You would have to plan on spending 1-2 hours getting your party together (cleric, rogue, tank, yourself and any additional classes you could find), you had to spend and hour or more fighting your way to the correct room (including unlocking the door), you had to hope there wasn't someone already there camping the room and then you had to kill stuff over and over until you got lucky. At bare minimum you would expect 8-10 hours to get the item, I myself had spent well over 20 hours and still hadn't gotten it in 2 trips.
So, I was looking and spending at least another 8+ hours for a 3rd incursion into the dungeon to get my JBB. That's 8+ hours in one big straight game playing session. A JBB was selling on Ebay for 50 bucks. 8 hours sitting playing a game uninterrupted or 2-3 hours of overtime work to pay for it. I signed up for overtime at work, made the 50 bucks, bought it on ebay and didn't worry about sitting in one room camping a spawn over and over.
_That's_ why people buy things with real cash, sometimes it's easier (or more time-efficient) to work your slave-job and get the cash, and bypass a time-sink in the game. New games since EQ have minimized the time-requirements, but it's still there and you need to compare the game-time to work-time to earn the same amount of cash.
