Another advantage of our sockets and plugs is the safety aspect especially with regard to children. The live and neutral apertures have shutters over them which move out of the way when the earth pin is inserted. The earth pin is slightly longer so the shutters move out of the way just as the live and neutral pins get inserted. This prevents children from sticking things into the socket.
And a switch as an added bonus!
The longer earth pin also ensures the appliance is earthed when the plug is not inserted all the way. It is the first pin to make contact and the last to disconnect.
And on the subject of the plug not being inserted all the way, the live and neutral pins have a plastic sleeve so if the plug is only half way in, little fingers feeling round behind the plug cannot get electrocuted.
The TR receptacles in the US (which I believe are now required by NEC in new residential constructions) have shutters over the live (hot) and neutral (groundED) slots. The shutters cannot be moved unless equal pressure is exerted on both simultaneously. Using the groundING pin to open the shutters doesn't work here, due to the large installed base of two-prong plugs. Every table lamp and double-insulated appliance uses only a two-prong plug.
I do wish, however, that our plugs had the insulated sleeves on the back part of the prongs like yours do.
For our three-prong plugs, the earth (groundING) pin is longer. But the quality of most plugs is so poor (thanks, China!) that the earth pin is easily broken off.
On a side trail of this side trail, it's interesting to note the difference in terminology between the UK and the US (and the NEC):
UK vernacular=US vernacular=National Electrical Code terminology
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Live=Hot=Current Carrying Conductor
Neutral=Neutral=Grounded current carrying conductor -- but doesn't really exist as such in the UK, does it?
Earth=Ground=Equipment Grounding Conductor (EGC)
The National Electrical Code (NFPA 70) did not even define "Neutral conductor" until the 2008 edition of the code, and at least one interpretation of the definition says that on a 120V circuit single-phase circuit, what's called 'neutral' in the vernacular isn't even neutral:
http://www.ecmag.com/section/codes-standards/neutral-or-not