The Programming of FFXIV? [somewhat lengthy]

[Chezen]

As an example, in the new expansion pack for WOW they changed the ways the classes worked (not too significantly but a pretty decent change for some classes), redesigned a lot of the original world, and added new types of quests, not just in content, but in style. Such as using a vehicle, quests that continue out in the field once you finish them, instances where the environment changes just for you, etc. Granted there are a few bugs, but for the majority it works well.

On this I don't see the same. They redesigned things in a couple of years yes, and it might not be that buggy, but it has hardly been a hit to everyone.

There's more to redesigning than rewriting code.