There has to be a rational explanation other than "because Alliance is populated by 10 year olds". I have been on alliance for two years and I have never played with a 10 year old haha. Everyone in my guild and everyone I have played with who I talked to in ventrilo was 20+.
I surfed around and found some theories that horde racials are geared more toward pvp as opposed to alliance whose racials are geared more toward PVE.
I enjoy PVP and I hold my own (meaning I am usually top three damage dealers) however, I would say that at least 9/10 times alliance lose in WSG, Arathi and Eye of the Storm.
I just don't get it.