My hypothesis is that the Chinese language (at least traditional) requires some kind of Unicode to be read. Is that not true?
That is a link from Wikipedia:
http://en.wikipedia.org/wiki/CJK
P.S. 11 June, 2010. I have just checked one more player, Ainol 9000HDA. Though officially it only has Chinese and English supported, it reads all kinds of Unicode, which I checked (UTF-8, UTF-16LE, UTF-16BE), provided it has a signature (BOM).