i was thinking same thing, i think blizzard should introduce new hero class for worgen and goblins race.
Makes about as much sense as:
Blood Elves not being able to be warriors but able to be paladins. (they must have not have had enough rage until now)
In all reality The only races that should be dks in large quantities according to warcraft III lore are humans and blood elves. Lordaeron was the only area hit hard by the undead.
So long story short: Blizzard does whatever the f**k they feel like.
The flufflore handwaved Blood Elf Warriors by saying that they all became Paladins.