anyway, dug out the original posters video... and i'll make it very clear i have absolutely no idea what happened in the studio, so the following is nothing more than my possible misguided opinion...
it seems pretty clear to me from the clip, they are not recording anything, just miming to an already completed recording, purely for promotional reasons... hence my lack of awe to the video...
ive no idea if both vocalists recorded at the same time in the same studio, or not.
what is known (ish), is which organisation put it on the tube, when they did it, and what they called it...
and here it is..
http://www.youtube.com/watch?v=MdCiZsbrsXQ