'Rehab' did just fine, the single didn't need to justify anything and was simply released to close the GGGB era. Perhaps a 'Breakin Dishes' release would have fared better in the charts but tbh that song deserved an early release when the album was fresh so that's kind of a moot point. Having Umbrella, Take A Bow and Disturbia all go to No.1 off one album, despite the releases, is very impressive and I don't think we should be bothered by an 8th single charting at No.18 when Beyonce's 3rd single in 'Halo' can't seem to even crack Top 30.