Thanks for the feedbacks, I have the EU version from amazon.de.
There is definitely a fault with either the screen or how it was put together, otherwise I'll not be able to notice it. Those marks does not show up on my Galaxy Tab 10.1, the original Tab or any my pervious mobile devices as far as I can remember.
I did note this don't affect the screen in normal use. Also the 100% brightness suggestion is to make the problem easier to spot, I normally have the screen at 5% in the dark, and we have no control over the brightness when the phone is switching off (when I noticed the marks).
I started this thread to find out what is the course of this problem and how widespread it is before deciding if I should send it back to Germany for a replacement/refund.
BTW, under EU consumer law, we have 21 days to return the device either for a refund or replacement from the seller, after that we might have to send the phone for repair.
Current mobile devices: ipad 3 3G; Nexus 10; Nexus 4; Xperia Z