As a follow up: I contacted Apple, and unfortunately, they won't replace my iMac's display, also telling me that it's not theirs but the vendor's responsibility to honor EU's warranty laws. That means if I wanted to have the display replaced because of EU laws, I should contact the vendor (however, I bought the iMac second-hand from an online store).
I went to an Apple Premium Service Provider nearby who said they would replace the iMac's display with a new one for 680 EUR.
I think I'll just bite into the sour Apple and replace the display myself. Do you know a good source for premium Apple parts? Preferably ones that came straight out of Apple's manufacturing, but without bugs this time.