Otterbox says 6s wont fit 6 cases.

I bought an Otterbox defender case about 3 months ago when i planned on getting the 6. Well, i held out for the 6s and figured i could use the case since all reports say the 6s will be a few mm difference in size. I called Otterbox just to confirm and they said the design for the 6s case is different. Seems strange that the 6 case wouldnt fit, no? Seems like all controls on the 6s are in the same spot as the 6. Otterbox cases always seem to have a little room to spare, so how couldnt the 6 case fit the 6s?