The summary says it all. Current FC Development gnome-themes 2.10.1-1 no longer contains any engines, so no more arch specific files. It could be changed to "BuildArch: noarch" in order to share more across architectures. Obviously, this only makes sense if there are no plans to re-introduce any engines into the themes package, which I don't know myself.
Just a quick reminder to know if this is a change that could be made, or if engines are to reappear in the package some day?
I saw there was a gnome-themes update today, and the content is still only xml, png and such. So it seems to me that it could really become noarch and be shared between i386, x86_64 and ppc to save some build time and disk space on mirrors.