Except most of Britney's hit singles didn't drop like a rock. And POM passed the 1 million sales mark within a few weeks of its release.
Keep Getting Better has been released for around six to seven weeks, and it still hasn't sold 500k. A flop.
And also:
Argentinian Airplay Chart[12] 88
Australian ARIA Singles Chart[13] 26
Canadian Hot 100 4<---------- Don't be fooled, KGB dropped like a rock there
Czech IFPI Airplay Chart 94
German Airplay Chart 12
Japan Hot 100 Singles 21
New Zealand RIANZ Singles Chart 36
Slovak IFPI Airplay Chart 13
Swiss Airplay Chart 24
U.S. Billboard Hot 100 7 <------------Dropped like a rock
Another country to add to the list: UK. Flopped at #14, her 3rd consecutive flop single in a row over here.
Oh, how Christina has lost her touch.