Appreciate the article. But if the ground outlet's ground is not connected to anything, should the reading give 0V instead of 4V between hot and ground and between neutral and ground?
Voltages are everywhere...if the ground is connected to a grounding rod (earth) and not to the neutral at the panel then you are simply measuring the voltage between the floating transformer from your utility and "earth" wherever your "earth ground rod" happens to be buried.
This is not a good thing - if you have a lightning storm and it hits the powerlines then these may carry very high voltages into your components within your home as lightning seeks a path to "earth"...in finding a path of least resistance it may burn something - sometimes even several items can get fried!