Actually, if you run a server and use MCPC+ then you can install worldborder, or worldedit, both of which have functions capable of resetting large swathes of land, worldborder is better suited for large scale resets though.
Well, Etho is a builder to the core, even if he happens to also take joy in making contraption, which makes Minecraft a great game for him.
The details he puts in these floating islands is incredible. like the "cave entrance", or how he put grass over the edge to make it look even better. He also chooses to make the islands based on the most awesome structures that Minecraft can generate, not the average plain or mountain.
Most of us would make a big chunk of land in the sky, mostly spherical/conical for the down part, and relatively flat at the top.
But he did use a method that is reusable by all those that wish to take great deal of time to make things look nice. Multiple fillers, tons of stone, a jet pack and a mining laser on explosive mode.