Thanks for bringing that up. Neither djp or I could find where it says / is an ID3 standard for separating artists. Either way Windows Media Player is a poor program for sorting music in the first place (it isn't even intuitive how to show disc #), so it's at least OK if we don't cater to that standard. Same with RealPlayer as Brad referenced.
All of that aside, / just isn't in common or trending enough usage to bother using it. It's the same reason we don't use OGG. OGG is good, but doesn't have enough support. If anything else comes up that would in fact be successful addressing this issue, definitely let us know.
JUST FYI, I've basically looked at iTunes/iPod and Winamp as the two standard MP3 players. If there's any other broad-use robust MP3 player I should look at, lemme know.