WHS wasn't out in 1999. The latest update for it was released yesterday.
Amazon UK as one example don't even stock boxes with Home Server installed.
Companies who are building similar products aren't using Home Server, instead opting for unknown faceless software.
Acer, HP, Asus, VIA and Lenovo are all using WHS for their Time Capsule-like solution. And then there's some smaller outfits like Tranquil.
No idea if it was a commercial failure. Seeing how they're making a new version (it's in beta), it can't have been that bad. I just wish they hadn't botched up the whole reliability thing at launch and then waited a year or so to patch it.