Notice the black insulating shields on the two pins of the new style plug top right - the new plugs are designed like this so that when the plug is not fully inserted into the socket outlet then any part of the pins on view and exposed are insulated so metal cannot be touched reducing the electric shock risk. This safety feature is not on older plugs meaning a higher shock risk when not fully inserted into a socket outlet.
Click for more safety info on plugs and extension leads.