And it had two excellent M-Rated games within a year: Eternal Darkness and the RE remake. I think it's more perception than anything. XBox is periceived as cool. After all, it has the most power, so it has to be the best system, right? But graphics and gore don't make games. The Xbox had only one game worth buying it for at launch--and for most of it's first year.
THe GC had two at launch, and two more by June. Only perception that Halo was somehow superior itself to several quailty games saved the Xbox.