There are conditions in EU and other countries where an Earth wire is not essential. Generally, it is omitted when there are two layers of insulation between the incoming AC side of the power supply and the laptop connections. This is called "double isolated" and is marked on the PSU with a symbol of two concentric squares. A high voltage test, typically 1.5KV for 30 seconds is carried out between the AC and DC sides to check the insulation is up to standard. Sometimes the Earth is still needed when double isolated if local safety regulations demand it.
Brian.