I've come across other claims that dogs are one of the few, if not the only, species that has evolved to understand human emotions through facial cues. A dog will look you in the eyes to understand your intentions. Dogs understand when you're happy, angry, or distressed simply by looking at you, no so much by your overall demeanor. 

A cat can understand you shouting and making menacing movements, but it will probably still climb in your lap indifferently for warmth if you're crying. A dog will actually understand you're upset. 

The interesting thing is that we've done this at a genetic level through selection. If you look at a wolf and a pug and consider the differences in appearance and behavior it's pretty fascinating. Especially in the short amount of time it's taken.

One of the reasons I've heard for why dogs are like this and cats are not is because we selected dogs for this behavior, whereas cats have selected us. We weren't as involved in selecting which cats we wanted.