Final Fantasy XIII and Final Fantasy XIV being released in the same year have no bearing on one another. There is absolutely no significant bleed over between their staffs, so efforts made towards the game are entirely independent. I sincerely doubt money is an issue for Square Enix; they can, after all, afford to purchase a struggling developer like Eidos. They're a business, and they wouldn't put down that kind of money unless they were confident they could afford to turn a profit on such a large investment.

Issues of time for the game, as Rostum mentioned, are apparent. It's become pretty clear that the development team was pressed to release the game ahead of its schedule. That's most likely an issue of the upper management putting pressure on the team, though, and has very little to do with FFXIII's release unless possibly FFXIII's disappointing sales numbers made Square Enix's management push harder to get FFXIV out. That would make sense, I guess, since MMORPGs tend to be massive cash cows.