As of the 2011 model, all second generation xBs have been built w/ cloth seats. That is how they left the Kanto Auto Works' plant in Iwate, Japan.
The Release Series models have had a special cloth w/ dots that reflect the exterior color. The RS 5.0 had yellow, RS 6.0 had red, and RS 7.0 had a purple/blue. Interior shots of the Voodoo Blue RS 8.0 haven't been released yet (as of typing).
Any leather would have been installed by someone after it left Kanto, whether a dealer or owner (or some other entity). Some dealers have a good shop install seat covers (whether glued in or slip-over- our seats don't have the metal framing in the foam for hog-rings, as the seats have the foam molded onto the foam).
If anyone knows of a model (however limited) that did have true factory leather, let me know. So far, I know of one tC special model (a Release Series) model (the charcoal one) that had leather seats. All the other Release Series and other Scion special run models, as far as I know, had cloth seats as built.