The second you popped the seals, it isn't new anymore...that's my take on it. it was handled by someone other than Lego, in the aftermarket. It's no longer new at that point, in my opinion. Like others have said it's a pretty touchy issue.
I understand the bricklink system and why people list the way they do there, especially due to the volume of loose pieces. There is a difference between buying a castle wall from a 1990's lego set that's yellowing and buying a vampyre castle wall from a freshly opened set. In my opinion, they are both still used, but to a different degree. In comic book grading, no comic that was handled by someone's bare hands would be considered mint anymore. But then again, it wouldn't be considered "fair" or "poor" either, if they touched it once and put it directly into a sleeve or whatever. Maybe Bricklink needs a more robust system, I guess.
On Ebay, I stand by my opinion that opened items should never be listed as new, and I'll never sell something with the seals "popped" as new. I especially wouldn't sell a set that's missing pieces as new, even if I exclaimed it was missing the pieces. It may not be deceptive if they explain themselves, but why list it as new then? It mucks up the listing system as previously mentioned - you go to search for a new item and you end up with a bunch of opened, parted-out Uruk-Hai walls that people still want to claim as new after they removed half the contents. Doesn't feel new to me.