Eric is correct. The neutral wire from the pole and the ground wire in the house serve two distinctly different purposes. The fact that they tie together at the service entrance panel tends to confuse things, but they are for different purposes. The neutral wire (wide blade on the plug) is one-half of the circuit to carry the operating current for the device plugged into the outlet. The ground wire is for SAFETY. It is intended to provide a second layer of protection in case there is a problem with the equipment somewhere in the house. Once upon a time I read a nice article explaining exactly why they used two wires connected to the same point at one end. I couldn't find it for this discussion, but you can find a lot of info on the web if you want to continue the search. Otherwise here is one reference: <http://www.homeinspector.org/resources/journals/Intro-Electrical-Grounding.pdf> Doug Reed.