From that thread...
Originally Posted by Fiery
Looks horrible to me. He has to lean forward all the time, and has very limited range of motion for his arms, especially when playing cross handed. Someone should tell him what happened to Phil Collins because of bad posture.
Something that Jack mentions in the White Stripes' "Under Great White Northern Lights" is how when he plays his guitar, he is constantly fighting with it. His guitar will go out of tune very quickly, even multiple times within a song, so he has to re-tune and battle with that as he plays. Also, if he has to go from a keyboard to the piano he'll purposely put it farther than is comfortable for him to jump from one instrument to the next, to make himself push for it.
I wouldn't doubt that he maintains that same mentality while playing drums as well, making himself reach for things.