Yeah, but again, there are no such magical diseases in the Warlock class. And game mechanic wise they are different from each other, because the DK can spread his disease to other targets easily, and you must use certain spells to dispel diseases. For example, The Monk spell Detox will dispel diseases and poisons, but won't dispel Magical DoTs like UA and Corruption. Meanwhile Dispel Magic will remove UA and Corruption, but won't remove diseases.
The only thing you've proven is that you can't tell the difference between a magical DoT and a disease. DKs are plated Necromancers. Guess what? They have several disease spells and spells that manipulate the dead. Warlocks have no such spells because they don't practice necromancy.You're so hung up on "Necromancy = Undead" when that's already been proven that Necromancy is so much broader. Next you're going to tell me that "Harnessing the shadows into bolts of incendiary energy" could be used for Fire Mages.