Those are useless for ppc, mplayer should not depend on that, I believe -avi should be in the default ppc USE
mplayer ebuild doesn't mind of USE="avi" :-( it should
I will double check this tonight, but AFAIK I am able to use all the win32 codecs with my PPC at home (it's just file formats not binaries). I build with USE="avi" and got usable items IIRC.
NOTE: WIN32 codec DLLs are not supported on your CPU (ppc). You may encounter a few AVI files that cannot be played due to missing opensource video/audio codec support. from mplayer ./configure output
Ok... these codecs do not work on ppc, you are right there....but without them mplayer will not install.. You will have to live with the space they take up, removing them is not a good option IMHO.
Also it is current impossible to remove those codecs even if it was desired for a single ARCH at this point in time without nasty hacks.
Is it currently more feasible? I'd suggest to make win32codecs an optional package for all architectures. It's currently not possible not to install it when installing mplayer, and I simply don't want to have to do anything with Windows.