Guess we'll have to disagree that it was contradicted in game, I'll use common sense, you use something else.
You also claim that warlocks used to have sense demons in response to someone speaking about spectral sight not being exclusive to Illidan. I think you'll find that sense demons isn't the same thing as spectral sight. Spectral sight is the unique type of vision that DH's have after removing their eyes. It allows them to see everything, not simply demons as sense demons did.
There's nothing that says this sight can't be granted to someone else for a time, as a matter of fact, sindwellers questline makes that abundantly clear. The issue still remains however, that you seem to know very little about the actual lore for someone making bold statements.