What Trulli did was correct and MS wasn't. He overtook using the outside. Trulli was on the racing line and therefore shouldn't budge for MS; that would be illogical on his sense. For some reason he wasn't penalized for this move.
At Imola last week I have to say Michael's move was the same thing. He kept to the line and JPM tried to overtake on the outside. From the video I have, MS appeared to correct his steering and it happened that JPM was in the way. MS did not (and shouldn't have) obliged to JPM's move or he too would lose a position.
Trulli did not shove MS off the road and remained on the line. Michael was just desperate to get some points so he passed on the outside in hopes of not being caught. It just happened the outside wasn't grass so there is almost no loss of grip or speed. He is lucky he got one point; the blown tire and a drive through penalty would have murdered him.
I believe MS did not shove JPM out of the way. He remained on the line as well and even though he "appeared" to be correcting his steering, the fact is that JPM was caught outside of the racing line when it happened.
MS got away w/ Silverstone for some strange reason, but in this case he didn't seem to do anything wrong. Adelaide 94 on the other hand...