Its easy to smile when your teammate has problems every other race and you are not even slightly in the WDC battle. He is a great guy, but he has much less to worry / get angry about than those two.
The fact that the disqualification, pit stop blunder and subsequent grid drop is no longer at the forefront of people's mind is a testament to Ricciardo's attitude and professionalism. Couple in the 'tough luck' episode and I think he's had just as much cause as Hamilton / Rosberg to start sulking.
He has arguably the toughest job this year to come into RBR and challenge Vettel. Monaco has just highlighted that drivers deal with pressure very differently.