The uranium at the Vinca institute was the reason NATO didn't bomb it because they worried that if they bombed it, it might cause serious problems for the rest of the Balkans. They actually stated something to that effect.
After the uranium has all been removed, I'm sure there will be no qualms about bombing Vinca if ever there is another airwar over Serbia. So it is no wonder that the U.S. paid for the removal, because it frees up another bombing target.
I vaguely remember during the great 'bombing for freedom' campaign back in '99 that there was a story alleging that the Serbs were in possesion of a 'dirty' bomb. I'll see if I can dig it up... Serbs could use nuke-laced arms (Washington Times)