It was a closed Xbox 360 server that couldn't connect to the PC and PS2 versions of the game.
The only game that I can think of now that has had cross platform gaming for 360 is Shadowrun for 360 and PC.
completely wrong
not 100% sure, but i believe the Play Online service SE had for FFXI(and a few other games), that was require to play the game, had something to do with it. Since SE no longer plans to use POL for any more games, it can't be used to play ffxiv on the 360.
Also FFXI recently had its level cap increased to 80(from 75) and will be at 99 by the end of this year, fortunetly new content over the last few years has made grinding much faster from 1-75 and the latest Add-on allows whole alliances(three 6 man parties) to get absolutely ridiculous xp/hr