Artistic differences!
It all came down to an argument about the White Stripes. Remember them? One band member absolutely loves Meg White's intuitive, innocent, child-like and musically crazy drumming skills. Loose, sloppy. Short of technique, but pretty amazing. Feeling trumps technique.
The other band member thinks her sloppiness, her loose-ness, is messy and terrible. No skill, no technique. Sinks the Stripes sound. Technique trumps feeling.
Put me, of course, in the first camp. Love Meg!
UPDATE: As for Jack, no question. Meg and her intuitive approach to the drum kit was the heart and soul of the White Stripes. Check out his conversation with Kot & Derogatis on Sound Opinions to hear it first-hand!