As far as the Kalimdor quest line goes I would think it is because you are playing an Alliance toon? These are open the first time around but not after.

I don't have a Darkmoon tank so this has been my set up for Farmer Nishi. Mirror Strider (1,2,2) Carry pet Nexus Whelpling (1,1,1) Vs. Siren: Pump, Cleansing Rain, Pump, Water Jet Toothbreaker: Water Jet, Pump, Cleansing Rain, Pump Brood: Water Jet, Pump, Pump, from here just be careful not to kill ...

For the 20 plus lvl's take 2 25's and the lvling pet to the new island. Start the fight when your first 25 dies switch to lvling pet then switch right to the other 25 finish the fight. Makes it so its almost one lvl per fight.