EA is a company that breaks the law repeatedly and one of the first ones to go "We hate people that sell games after they played them, which legally they're allowed to do so lets include a code in any of our games that go online so we can make more money, but supply subpar games that are usually the exact same except a slight difference in our storylines"
FFXI is the same software, so you can legally use that software on any format. Just as you can use a PSX game in an emulator on a PC if you want to, you just need to own a version of the software.
The only time this is different is if they released a game that was once out on the PSX and remade it, such as Resident Evil (which they did PSX>GameCube.) Then you need to buy the game on the Gamecube before you can use other means to play it.
