OK, I'll bite
This action is not surprising given Ecclestone et al's antagonism to McClaren and vice versa of course...but it is a bit surprising that they did it in first race.
Hamilton witheld some radio communication apparently...so 'lied by ommission'.
But think about it...what did he have to gain?
He was probably 4th at the time the SC pulled out. Trulli went wide, Hamilton slowed but still had no choice to pass...technically correct so far because Trulli made a 'mistake' in SC zone (similar to Vettel being passed).
McClaren are then worried that he 'may have' done an incorrect overtake (they were not sure), tells Hamilton to slow down and let Trulli pass---this did happen---you can always sort it out afterwards.
Hamilton goes to stewards, tells them that he was in 3rd and slowed down, omits the McClaren orders (radio comm) and they give Trulli penalty.
These stewards either have no idea how to make a penalty fit a crime, or they have their own agenda's.
Firstly Trulli should not have been given a penalty..the positions should just have been reversed.
And then when they found out about the instructions (because hamilton was quite overt about it to press) ..what difference does it make why he slowed and who told him to do so.
What they should really be concerned about is that when both Hamilton passed Trulli (Trulli's mistake) and subsequently Trulli passed Hamilton, both drivers were not 100% sure they were doing the right thing.
So quite obviously their laws are not clear enough at all that drivers do not know what the correct thing is.
You could even see this when Vettel was down to 5km/h on three wheels, drivers were still 'scared' to pass.
But its not like F1 to admit that they have a problem with the clarity of their laws in practice.
cheers