I'd argue that you've gotten what you've paid for with that monthly fee; you played for the month you paid for. It doesn't guarantee you anything beyond that.

I'm beginning to hear rumblings that purchasing Vision of Abyssea may be required to access level 76-80. All Square Enix has said is that there will be no limit break quest as we understand it, but that there would be a "requirement". People have noticed that with each Abyssea release there is also a planned level cap increase and some think it isn't merely a coincidence. I don't know how I'd feel about that.