Loot systems in games can be quite a gamble -- similar to slot machines in many ways. Players' efforts to overcome encounters for a chance at a reward are comparable to the coins required to operate a slot machine.
As the amount of effort required to achieve a chance at reward increases, so does the metaphorical bet. This system can introduce the addictiveness of the casino into the MMORPG, but its purpose goes beyond that.
Rollercoasters That Never Go Down Are No Fun
Chance in a reward system can help reset the psychological thresholds of expectation for players. In this way, it combats the bloating of the rewards required to sate players as they progress through a game. However, a fine balance must be maintained as adding too much chance in a loot system can result in too great a loss of predictability, which can diminish the effectiveness of rewards, making them less capable at reinforcing players' behaviors.
Remembering back to my experiences in Warhammer's beta, I found its public quest reward system very frustrating. When determining who was to be awarded at the end of the quest, player contribution was taken into account. But a random number was added to this contribution score before the tally was made, which meant that the highest contributor often went home empty-handed.
My Other Vehicle is an Epic Mount
If you are skeptical about how killing mobs is like playing slots, allow me to recount a sad period of my life. There was a time, albeit a short one, in which the epic flying mount that my character flew in WoW: The Burning Crusade was worth more than my car.
I was only able to afford it because I lucked out and found two purple items (epic quality) in one day, which I sold for a tidy sum -- in game currency worth about 400 US dollars. Meanwhile, a guildmate of mine was reduced to purchasing hundreds of dollars worth of gold to afford his epic flying mount. He had a job and could throw around that kind of cash. I on the other hand, was gleefully unemployed at the time and could spend many more hours on the game than he could.
In the end, we both put forth similar effort to achieve the same result, but mine, which was based exclusively in game, also involved a lot of luck.
Tearing into some Tinfoil
Another form of gambling that gamers crave can be found in the business model of booster packs for trading cards. There's an undeniable excitement when you're tearing into a new pack. The contents can be worth 50 cents or 50 dollars -- either way, you pay five. This thrill comes from a purely luck-based form of gambling. There is no skill involved in opening or selecting a pack, and yet it works.
The MMO industry can learn a lot from booster packs, particularly in how the thrill of chance can be introduced into the microtransaction model without flatly turning the game into a glorified casino. Other than peddling essential consumables, such as health potions, teleportation tokens, and item enchantments, there may be no better way to get players to pay several times for the same in-game items. Just make sure to keep purely luck-driven elements away from actual gameplay.
The Games of Chance Paradox
Ironically, most games of chance are about minimizing the effect of chance. Poker players will try using mathematics and psychology to gain the edge on an opponent, and a dungeons and dragons expert will rarely let his fate be determined by a single dice-roll.
MMOs should contain predictable chance in their loot systems, little if any chance in their actual gameplay, and can contain as much chance as good judgment will permit in supplemental income strategies.