Xbox Live as a subscription service seems to be the biggest money maker, according to an article from Bloomberg. The Live service over this last year is estimated to have broke the $1 billion dollar mark collectively through subscriptions, Movie and TV show sales, and DLC.
According to estimate of the last year Microsoft earned around $1.2 million dollars, which is most likely a major contributing factor to Sony's decision to start the paid PlayStation Plus subscription service. With an average of 25 million subscribers to Xbox Live, that number accounts for just about half of the profits in total, that's $600 million in subscription dollars.
With this heavy influence on the subscription service, hopefully we won't start seeing insane subscription ideas coming around like Bobby Kotick had suggested with Call of Duty. Let's just hope we don't see any corruption with Sony or Nintendo beyond a secondary service.