FF14 Screen
The "closed" Xbox Live platform has impeded the advancement of console MMOs on the Xbox 360. Square Enix has had to stop development of a Xbox 360 version of Final Fantasy XIV due to the restrictions of the Microsoft console and Square Enix isn't the only developer that dreams of tapping into the potential of having an MMO on the console.
However, developing a console MMO has always been a challenge, especially for the Xbox 360. Introducing platform holders into the business of MMOs causes revenue to diminish. Companies like Microsoft want a cut of ongoing revenue generated through the game's subscriptions and/or micro-transactions.

Xbox Live, considered to be the best console online service, has seemingly closed itself off to MMOs. In 2003, Final Fantasy XI was released as a console MMO on the 360. However, according to Square developer Hiromichi Tanaka, that was a one-time only deal to promote Xbox Live, which is now much more established in the gaming community.

Tanaka commented further:
"Microsoft's guidelines were not so clearly defined [back then]."
Square is trying to speak with Microsoft and negotiate. If an agreement could be reached a 360 version would be released. Unfortunately, it seems unlikely that Microsoft would open the golden gates of Xbox Live so that 360 owners could experience Final Fantasy XIV on their console. So far, Microsoft's strict policy has prevented Square's attempts to break through.
The PS3, the console with a more open online service, is scheduled to receive Final Fantasy XIV next year while PC gamers will be able to jump into the fantasy world this September.
Source: CVG