If memory serves, Sanderson turned in his completed draft for TGS in April for a late October release. The equivalent for a March/April 2011 release for ToM would entail him turning in his manuscript in September or October of this year, or maybe August if he wants an extra month of editing. To my mind, given that he's 82% complete and it's only January, either 1) he really expects to need ten to eleven more months to finish his draft (amounting to progress of only about 2% per month), which seems unlikely even if one plotline does need to be revamped; or 2) he will be finished before September/October, but Tor wants to delay publication for some reason.