While it would be nice to get both versions when you buy one of them like Valve did with Portal 2 on PS3 (the PC version did not give you the PS3/360 version though) S-E want to make money like any other company out there. DCUO only allowed you to download the client for free once it became free to play, before that you had to buy either the PS3 or PC version and there you could not play with the same account on both, you have to make two separate accounts.
So while it would be awesome if they gave current players a PSN code to download the PS3 client for free they would lose a ton of money on that and I doubt S-E is willing to lose more than they have already on FFXIV. :P