It's my opinion that people like to see their pets happy, and since pets get excited or enthusiastic when fed (and'll do tricks, begging, etc.) they indulge their own feelings by overfeeding the animal.
Pets aren't the same as humans, they don't need three squares a day to be happy and healthy, in fact, overfeeding will make their lives more difficult ultimately. It's ok to eat in front of your animals, I think some folks feel guilty or glutenous if they don't 'share' or feed their pets whenever they eat.
I've heard that many dog breeds have a feast or famine metabolism, they can intake a tremendous amount of food in one sitting, and can also go extended periods without eating with no ill effects - a trait they retained from their wild ancestors.
Come to think of it, most people probably don't really need three squares a day either, probably just a societal hold over from back when folks where a lot more active in their day to day life.
My beastie is certainly no slouch in the panhandling dept. but he doesn't bother with us as we (duh!) never give him anything. Good old lamb & rice formula high-quality dry dog feed does the job just fine. Dogs are none too thrilled with the stuff and therefore eat no more of it than necessary. What HE wants most of all is action. I've been a good boy and take him for two spins a day. One if I'm inclined to march him down for a goodly brawl at the local dog park.
My last dog had constant food and regulated himself. Never got fat.
My current dog would eat till she burst under the same regimen.
Ultimately a fat dog is the owner's fault with rare exceptions.