What's the practical difference between Thing-Talker and World-Talker?

See the title for the question.

Since most mundane nonliving objects are presumably made of some mix of the pure elements, I can't seem to come up with anything you could shapeshift into with World-Talker that you couldn't creatively approximate by finding something made of mundane matter and shapeshifting into a creature based on that object.

Unless the pure elements bring with them with some kind of long range or general elemental manipulation powers, or are just nebulously more powerful somehow without spcifying how, I just can't grasp the difference between them when you consider the end result you are trying to achieve, rather than what you do to get there.

Basically, what is the difference between shapeshifting into an earth "elemental" made of your garden variety rock and shapeshifting into an earth elemental made of pure elemental earth?

Now I understand that the thing with most of these kind of questions is that it comes down to the group and the game fiction and what your personal Dungeon World is like, so I'm asking for your interpretations on how World-Talker is supposed to improve upon Thing-Talker more than a definite answer.

I'd allow supernatural moves in elemental form that I wouldn't accept in rock- or water-form (and I don't think I'd allow 'fire-form' or 'air-form' for Thing-Taker)—flinging rocks, talking to water spirits, that sort of thing.

I think they're an excellent question to turn back on the players. "So, Niri, you took Thing-talker, what do you figure are the restrictions on that? To you, how's that differentiate out from World-talker?" I think the answers could damn near provide a front themselves.