I guess it depends on the original. In regard to the paint job, Tim already said there are purposeful differences, not to mention when you have an item mass produced in China, you simply aren't going to get the same quality paint job as a hand-finished piece. In regard to the paint... I look at the price... and for $500, I can add a bit more wethering and decals myself.
In regard to the details like the knob and the grill detail, I can't help but wonder if a different base was used. The addition to the grill piece makes me think that this piece may have actually fallen off the prototype we saw... who knows. I can't explain the difference in the knob. As far as the screw, easy replacement for me.
Is this a perfect reproduction down to the last detail? No, but at the price point, I think Weta is so far ahead of its peers it isn't even funny. I can't believe they managed to get this done with relatively no clean up work on the original. If you want a comparison, go check the eFX Vader helmet thread and all the concern on sanitizing the prop. This was my main concern as well and Weta handled it superbly.