Wintergrasp is occupied by the Aliance 90% of the time on Icecrown. There are more pvp guilds on the Aliance than on the Horde, a fix for this would be to add a increasing buff to the losing faction, like lose once - get buffed 20% HP and Damage, lose twice in a row - get 40% hp and damage. It's still going to be hard for the Horde to take Wintergrasp because the ally side is made of bis pvp premades and the horde side is made of badly geared 16k hp people.
What? This already exists. It's called Tenacity, and you can get it either through losing twice in a row, or having fewer players than the opposite side. You get 18% more dmg and 14% more dmg for each consecutive loss after the 1st one.