Petrol cars must have this socket as required by law.
Diesel passenger cars are not required to have it until 2004. For diesel commercial vans (like the Transit) it's 2007.
It's there because that is easier and cheaper for Ford to manufacture.
Communication protocol is Ford company protocol.
And No, your obd2 scanner won't work on it.

By the way, obd2 is something that exists in the USA and Canada only. It has no meaning in Europe and no car here (except imported cars from the USA) will comply with obd2 rules. Over here we have EOBD, which is very similar to obd2, but in some key areas it differs - like the starting date and when to set a diagnostic trouble code.