nordlead on 21 January 2010
WMV is a microsoft format and Sony probably didn't pay the licensing fee to use the format. (not a lot of companies do)
EDIT: as forevercloud stated below, you have to do the liscensing thing (lol, I've never used my PS3 for videos other than off PSN 
)
As for AVI, AVI is really a wrapper and it could be using one of any number of codecs available. Depending on who encoded the AVI file it may not be compatible with the PS3. On PCs it isn't an issue as you just install another codec.
