Its a bit gear, gear, gear,
Its a bit tactics, tactic, tactic,
And then its all horde.
Imagine this scenerio: 4 horde incoming to Stables where 3 alliance are defending. The horde priest pops in and fear bombs the flag. The four horde start picking people off one by one while the 3 alliance are running around like chickens. Then the Undead warlock howl of terrors everybody for 18 seconds. The alliance die and the stables are capture. 3 dead alliance, no dead horde. Now this battle could go in any way all in favour of the horde. Say the shaman drops his slowing totem, 3 alliance movement speed is decreased, and all are kited. The tauren warstomps instantly stoping all spell casting and attacks for 2 seconds the frost shocks everybdoy to further slow them.
Now imagine this, 4 alliance attack the farm with three horde defenders. The all come in on the flag and the priest fear bombs them. The two undead WoTF out of the fear and are instantly back in combat. You go after the tauren shaman who is still running with fear on but the moment he takes damage, he is out of fear and warstomps to instantly put the 4 alliance out of commission for 2 seconds, enough time to pop out a couple of totems. The two undead are now hammering on the preist, and your priest is dead. Its now a 3 v 3 fight and the alliance is effectively crowd controlled through the use of totems and frost shock. The shaman kites the alliance around while the undead warrior\rogue\warlock\priest (whatever the case may be) pick off the alliance who are left and being kited one by one.
The cross server BGs have shown me that Horde > Alliance in small PvP battles, not because of skill or gear, but because their racials and classes are better suited for it.