It has nothing to do with twinks and everything to do with speed.
Having now played both Horde and alliance PvP extensivley I reckon I know the reason horde always win lower level wsg, it's due to the fact that horde have access to shamans and druids which each have access to travel forms. This in its self isnt a game winner, the tactics they use however is.
Next time your in a WSG I suggest keeping an eye on the horde druids and shamans, they instantly travel form up the external ramp towards the ally graveyard and into the flag room from the top. After getting the flag they exit the room via the graveyard and bobs your uncle Point 1, rinse and repeat till win.
Of course it's not quite that simple but essentially thats it, horde realise it only takes 1-2 shamans/druids to capture the flag where alliance all run for the flag room as individuals leaving no defense. This whole tactic falls apart if alliance leave a warrior and a rogue in defense which they never do as they are to busy reaping HK.
So wanna know how to win low WSG, leave a small defense 1-2 classes capable of stunning/slowing, leave capturing flags for the druids, everyone else hold the middle and get your own flag back as it comes out your base.
As a side note I might add the healing activity on the horde side is far supperior to the allaince side, solution-roll a priest and actually heal in wsg.
Now it's 5.30am time to go to work, laters all.