Im sure i read some where before his first london appearance, that he had done a lot of work on a treadmill in front of a mirror to alter his style, from the more aggresive footstrike he had when racing on the track to the more mid foot strike he has now.
it makes sense a marathon is a hell of a lot further than 10k so your running style will be different, eg. a 400m runner runs differently to a 1500m runner,