Patents

I can't think of a current MP3 player which does MP3 decoding in hardware. One of the reasons
for the huge delay before the not-release of Rockbox 3 was the implementation of a software
codec layer (with the corresponding explosion of supported codec format), because the Archos
was the only platform Rockbox worked on which had a chip to do it. Everything else uses CPUs:
it's cheaper (modulo patent rubbish), more flexible, and with modern CPUs faster too.