On the second one:
Goblin starting area starts up right before Deathwing blows things up.
As for Worgen, they've been behind a wall for I forget how long. That wall doesn't open up until Cata.
Both are in game story limitations: monks wouldn't make sense for either because of this.
Even though Forsaken can be priests, they only are holy/disc due to gameplay reasons. Don't recall if I've ever seen a healing undead priest NPC before. Paladin's use nothing but inner light spells- something Forsaken can't wield.