My understanding was that the tires were cold and hence a little underinflated. When he went into the corner, his chassis bottomed out taking the weight off the tires, causing them to lose traction. I think they disproved the theory about the steering column breaking, but it was a while ago when I read all about it.

For those interested, here is the video of the crash:
http://www.cineca.it/HPSystems/Vis.I...ovies/out5.mpg