Maybe they figured out that sales vs support calls didn't make it worth the effort of 'officially' supporting 98.
I do support for product and I wish M$ hadn't extended 98 support, I'd get less calls. I also wish we'd drop support for SCO then my calls would really drop but thats another story.
XP is the best OS M$ have made but if more games would run on Linux then I'd remove my XP partition and just use Linux.