Ah so it wasn't the Rio after all...
I always thought about Rio, but then, I heard about the Rio MP3 player until late 2000. Hell, 10 years ago I was leeching mp3's from FTP sites that came and went around the net, the olden days before P2P, Napster or Audiogalaxy. (In my opinion, Audiogalaxy was the best of those first-gen P2Ps 'coz the "central node" managed all the file-finding and stuff, but that's another story.) Heh, I had a Walkman back then ... with "digital" stuff like auto-searching FM/AM stations, 20 presets, and AVLS (so I wouldn't hurt my eardrums with excessive sound).
MP3's were not "obscure stuff" by 2003. Anyone under 21 would have known mp3's by then, as when the format became "popular" (1998), it quickly spread amongst college and highschool students worldwide. Proof of it is that I returned from my school vacation to find lots of my buddies showing off their 300+ "CD-Quality" music collections fitting in 600Mb. Ok, my school went into a compulsory "student+laptop" program on that same year, so that and campus broadband helped a bit.
The iPod came out as a "rich kiddie" toy, nice but expensive, and Mac-only, which that alone excludes like 90%+ of the whole market. Even when it went Windows, I didn't like it because it's expensive, and the iTunes requirement. The quantity of mp3's I now have is so huge I prefer segmenting it into folders, and I copy those folders using mass-storage protocols instead. My sister's got an iPod, and prefers to let iTunes synch whatever there is to the iPod than spend 8 hours ticking/unticking checkboxes.
Me? I used to have my W300, with an iPod-ish menus and my only complain was having to traverse the lists. My current Blackberry has text-searching and the "trackball" so that isn't even a problem anymore. ;) I would've liked Sony to do the mp3 Walkman back then. Oops!