Hardwareguy, I believe that UL would test that receptacle to the same standard as any other receptacle ... which is not the same thing as using a screw-in adapter to the light socket.
IF such an adapter were used ... I think your point about the 600 watt limit would be on target, ant the receptacle would not qualify.
Paul - Sharp eye! Actually, over here the fixtures come with a short chain (as seen in the pic), and a simple string that attaches to the chain if you want a longer tail.
