SilverWook said:

The ending scene for Episode III was originally shot on location in Tunisia during production on AOTC, but was reshot in the studio on ROTS.

http://www.starwarz.com/tbone/special-deliveries/

Crews were dispatched to various locales to shoot background plates for Mustafar and Kashyyk, but it does seem the main unit never left the studio.

Whoa! Tbone (finally) updated his site!

EDIT: I feel kind of dumb, but judging by the news section, I was always looking at the archive site without viewing the new one.