[agrumpycow]

I find this really interesting as well. I can only speak for my own two dogs, they seem to communicate, as you said, through posture, eye contact and tail wagging which seen in-built.
They also learn techniques to get their point across. It makes my hubby laugh that I can listen to my dog grunting/whinging/whining (whatever you want to call it) in a different room and just from the sound I can tell what they want, food, water, to pee, etc.