There are too many challenges that MMO are facing so few developers braved the idea - but not for Blizzard's "World of Warcraft." Developers know that hefty expenses are only secondary to the challenge of retaining a massive number of players to make any MMO credible.

"World of Warcraft" proved that paid subscription is a lucrative investment albeit tons of risks. A $15 monthly fee might be too much for players if "World of Warcraft" had been a disappointment. On the contrary, the game has continually gained followers. In fact, there are claims that "WoW" has 2 million paying costumers at the peak of its popularity.

Come to think of it, "World of Warcraft" earned a staggering $180 million every month out of subscription. In 2016 alone, Blizzard earned a total of $9 billion if other "World of Warcraft" derivative business models are taken into account. Forbes reported that "WoW" players have dwindled over the span of 12 years, but it still has solid 10 million active players.

Game Revolution reported that apart from monthly subscription, "World of Warcraft" may have been earning more out of game expansions that usually cost $40. These figures can easily offshoot if revenues from merchandise, video games and even movies are considered.

One that can claim the competition against "World of Warcraft" is MMO shooter "CrossFire" who earned two-thirds of what Blizzard made. Even Nintendo's Wii Sports have to be bundled with hardware to achieve $6 billion revenue.

Gamers are comparing the success of "World of Warcraft" with the "Pac-Man" era in the 80's where the game cashed in $12.81 billion. "Space Invaders" and "Street Fighter II" also breached at least $10 billion in revenue during the same decade. Again, these arcade games have their shots while "WoW" seems to be unchallenged until today.

What could potentially be the next MMO superstar that has the potential to capture "World of Warcraft's" throne is "League of Legends." However, majority of its $1.6 annual revenue came from microtransactions and not from subscription as opposed to "WoW."