Why is there a live and a neutral in a wall connector?
Hot and neutral are the supply and return lines.  Ground/earth is a safety line and does not normally handle current flow. 

What defines a neutral is that some effort has been made to keep it near earth potential.  It is not quite at earth potential** and neutral is not ground. 

Now, some plugs and receptacles are polarized, either by virtue of differing pins (the wide blade on NEMA 1), or simply a side effect of having a third grounding pin not inline.  In that case, the appliance knows which pin is neutral, and can be designed internally with that in mind.  The classic example is a screw-in bulb fixture; the easily-touched outer shell of the socket is made neutral, and the harder-to-reach tip is "hot" and also switched. 

If its plug is not polarized (Schuko, GU10, GU24), most likely the appliance is required to comply with a higher insulation standard, so the appliance will be nominally safe even if the prongs are reversed.  



** and sometimes more than a little not at earth potential