I think he actually left out 4 major points (as opposed to 3). These are my guesses based on experience.
Economies - Not only do you earn points and level up but you may also spend them at your own will. For instance, look at the bounty system on Stack Exchange sites... I had a burning question to ask that was getting no feedback and had no reputation to spend on it, so I spend 4 days answering a ton of questions so I could post a juicy bounty (and it got me a great answer). There are players in China that play World of Warcraft as a full time job dubbed gold miners because all they do is run around collecting gold in the game to sell online for real money. The same was also true in Diablo II where some of the items were so rare than out of the hundreds of thousands of players playing at any given time over the course of a few years would only find a couple. The rarest item (a Zod rune) of which only one had been found after 3 years of gameplay sold for a reportedly 1100 USD on ebay. If games are the future of social engineering, than Blizzard Entertainment are poised to take over the world because they are the masters. I quit playing World of Warcraft after two weeks because I could tell that the game was more designed to have go on forever, be relatively boring and slow moving, while being designed to be extremely addictive (I had been through a pretty extensive Diablo II phase in the past and learnt that lesson).
Identity - Not only is it important to be able to level but it's important to be distinguishable as an individual. Whether that means that you use a alias as your handle or you use your real name. That's what made Facebook win over MySpace. By getting people to use their real names, not only was it easier to find your friends (past or present) online but, by attaching real identities to the handle, most of the trolling/trash talking/spaming/lurking stopped because the people taking part in it could be held accountable. Stack Exchange sites do this by adding the profile to each user's account. World of Warcraft does it by allowing you to customize your character in many ways to look unique. Tiger Woods Golf, as well as Nintendo Wii and XBox360 does it by allowing you to create a custom 3D avatar. Twitter, Stack Exchange, and many other social networks do it by allowing you to respond to a unique user by adding the @ prefix to their name making it easier to have a direct dialog instead of the typical 'talking to a wall' experience of commenting systems that don't use it (IMHO the single greatest simple innovation in social networking ever).
Scarcity - Blizzard have mastered this since the days of Diablo I with the 'normal item', 'magical item', 'rare item', 'unique item'. In the early parts of the game, normal items work. As it gets harder magical items become a necessity. Harder still and rare items become a must. Then unique items. Then (in the case of Diablo II on hardest difficulty) they went as far as to make it near impossible to beat without working as a team. As I remember the trade for unique items was a pretty brutal marketplace. It took a lot of work/time/effort on the hardest difficulty to gain worthwhile unique items and it was always a hard bargain to trade for them. World of Warcraft took this a magnitude further by creating the automatic-auction system that mimics ebay to sell items online over the course of a pre-defined time allotment.
Social Dependence - In World of Warcraft, It's a lot harder (sometimes impossible) and a lot less fun to play alone. That alone makes it necessary to socialize and group up with other players. In Call of Duty, if you have a decent team all with headsets you gain a huge advantage by being able to share intel on the other team and coordinate attacks. A lot of services sold today offer the 'sign up a friend and save x amount on your first bill' bonuses. Facebook offers the like button and ability to comment on other's posts. Without comments and approval micro-blogging becomes pointless. Ever since the earliest games, the multi-player option has always been a necessity because once you beat a game on single player, there isn't much point in beating it again (IE, the story line is over). Multi-player games enable humans to play together or against each other. In almost every game I've ever played multi-player, with an equal set of advantages/disadvantages the human is always harder to play. About the upper limit of a single player game for playability length is about 60-100 hours of content. Anything beyond that feels tedious. With multi-player, it becomes unlimited (or until the next great multi-player game comes out) because human strategy is dynamic. A top sniper spot on one map one day may become common knowledge in a week thereby making it an easy target. Sometimes, there are anti-strategies where picking a strategically poor position may be a huge advantage because it is unpredictable. The only games where a computer can consistently win are lame algorithmic games with really limited sets of rules and dynamics like chess (IE the computer can calculate every possible move and counter-move before playing out its turn). IMHO, chess is too simplistic to be a chess game. I prefer to place it in the category of mental masturbation. The best part about social dependence is, the game sucks without your friends so you have to get them involved. How much more viral do you get than that. That's how MySpace and Facebook became successful. Nobody wants to have 0 friends online.
