How do dogs know that showing the puppy-look softens us?

Or the question should be "Do dogs know that showing us the puppy look softens us?". The first time I noticed a dog giving a puppy-look was when I was playing with a neighbour's dog when he came over to my house. The kind of look that resembles that of the picture of Max below. This dog did it many times to ask for food. And at the same spot at the entrance of the house.

When I took Jon in, he too behaves like this, though he does not lie his chin on the ground but put his paws on the gate. He does this to ask for food. Then came Max. He does this immediately every time after I come home. He knows what routinely will happen next is a walk for him and Jon. I wonder why he does this? Is it a universal dog body language to request for things? Do they know that they are extremely adorable that will soften anyone; and that it will take a considerable amount of self-restrain on our part not to give in to their requests/demands - especially when it comes to food.

I welcome any comments on this doggish behaviour.