Basically becuase as "vile despots" go, Saddam was far, far worse than Milosevic by any measure, be it in filling mass graves with victims, unprovoked attacks on neighboring states, supporting international terrorism (Saddam's support of terrorists has been conclusively proven, they're just not high-level Al Queda terrorists), oppressing religious and ethnic minorities, the actual use of WMD (no fewer than 10 times, with tens of thousands of casualties), and in operating a huge and sophisticated police state.
Of course, in this line of discussion, we're just considering how evil a particular despot may be, not the threat they may pose to US national security. Not only was Saddam clearly far more evil than Milosevic, in the view of the Bush administration, and I would certainly agree with them, Saddam was a far greater long-term threat to US national security as well.
Current Events » in reply to I don't think you get it
The Yugoslavia analogy actually greatly bolsters the case for the war