How many homeowners have their dogs on a leash while they are at home?
How many times do I step over a leash when walking to a door to deliver? Many times.
When a dog is on a leash it is more of a "fixed object" issue and therefore limits the dog's ability to escape harm.
I guarantee that the owner of the dog would be more angry if you ran over his pet when it was confined to a certain, smaller area while on a leash and couldnt fully escape than if it had the whole yard available.
What does the owner being home have to do with you running over their pet anyway? The issue is: was the back necessary. If strange dogs are present you are backing to make your vulnerability less and the possibility of delivering that stop on the first attempt greater.
The owner of the pet often views their pets as harmless but we view an unknown dog as a possible threat.