I think its a bit harsh, especially the 25 second penalty. But their explanation is undertandable. Its not that complicated.
http://www.youtube.com/watch?v=RpqlEg19NK0Its really quite simple. Kimi was defending his posistion on the chicane. Leaving hamilton with the option of following into the next section and getting into his slip stream or trying round the other side, if there was enough grip or not,
He chose, chose being the key word, to cut the chicane, and simply took kimis slipstream to overtake after.
In short, he got an advantage by taking cutting the track, regardless of if he slowed down to resume posistion.
I felt quite bad for kimi tbh. That was his race till it rained.