This is such an odd issue. I struggled with it some when DH and I got married. Not because we lived together beforehand, because we only lived together for a few months before the wedding, and he didn't bring any "stuff" along because he lived with his mother before moving in with me. More because I'd been on my own since the age of 18, so I thought it was weird to be asking for household items after I'd had my own household for 11 years at that point.
What I did was to register for items that I didn't already have, because I'd had no need for them as a single person. Things like a buffet server (I didn't entertain much when I was single), formal china, a crockpot, etc. I did register for everyday dishes, because what I had at that point was three place settings that were mismatched and chipped and had been picked up at the dollar store. So, maybe I was rude for wanting to upgrade my dishes at others' expense?
Then again.. if the logic is that people who already have household stuff shouldn't be registering for or getting household gifts, then only newlyweds who have moved from their parents' houses to their marital household should be getting gifts. That doesn't seem right, either.