Why is the earth a viable return path for power distribution?
I think of the ground as many parallel high resistances paths, which add up to a low resistance.  Good earth connections (&lt;50ohm) usually involve a decent bit of copper rod in the ground, for an average pole top tranny you would probably have 4+ metres buried depending on soil resistivity and local regulations. Really good earth connections such as in a district substation are usually less than 5ohm and as such are excellent return paths.
From your house, the return path is back to the star (earthed) point on your service transformer, either via the earth or neutral wire depending on the earthing arrangement in your area.