It has been a while since the creation of the SPSlideShow web part, but I haven’t wrote the story behind it. At the time I was looking for a slide show web part, and I found few, even open source, but ALL of them were Flash or SilverLight based. SilverLight is good but not every enterprise got it installed, and Flash, well, I try to avoid Flash when I can, too many versions, with far too many unique problems (try using Flash 9.0.16 on IE6).
p.s. use the forum for bug reports.