WoW's improved its engine significantly over the years (includings the visuals of course) to compete with MMOs as they came and died out. Do you honestly believe the game would have survived if it still looked like what it did back in Vanilla, and things like animations and model quality didn't improve quite a bit? The reason they couldn't improve FFXI significantly was due to the PS2, but back when FFXI was released the PS2 was still in its prime, this isn't, and was never the case with the PS3.
As Yoshida stated, they want to compete with things like Everquest Next and all future MMOs, I don't know if you've ever seen that but the physics and visuals are very nice, and that was back in 2013. WoW is no longer the competitor it used to be, and I can see it dying down if Legion is flop like WoD. The PS3 was dead on the release of FFXIV (or rather, very outdated). The parts it's holding the game is quite clear, raids like CT and ST have to be separated with loading screens, areas are separated and isn't just one seamless world, and as the interview stated earlier, they can't have incredibly large scale FATEs (this would also limit their boss design in raids, dungeons and trials).
Yoshida has said he wants the game to last 10 years, and keeping PS3 around isn't the way to achieve that. By the time 4.0 rolls around it'll probably be 2017, and the PS3 will be 10 years old. No one should expect 10 year old hardware to keep being supported then, nor should they demand stifling the game because they can't move past decade old technology.