You're misquoting everything I said. I said cover does not allow you to HIDE, since cover does not stop an opponent from 'seeing' you.
Now you're talking about a separate sense, where the rogue does or doesn't literally have anything to hide behind, when no one is around to oppose him finding a good hiding place.
Yes, I'm saying in 'combat' ducking behind a desk doesn't make enemies go braindead, and not be able to fathom where you are. They know exactly where you are, you are behind the desk.
Now, when you enter a room and someone in that room had been hiding, its a GM's call what you're hiding behind (or who cares). You're now bringing up a case where there is 'nothing' to hide behind, which is again a GM's issue. If he wants to say that you 'cant' hide in broad daylight, or in an empty room, so be it. But the rules aren't talking about this, they're talking about taking the 'hide' action in a normal circumstance.