This is due to the fact that as the higher the rating goes up the higher the skill level cut off goes up. The boosters pilot it because they are all rank 1 and gladiator. They can beat anyone at any given rating and they can boost up to 3k rating even!
Our boosters have competed at tournaments, been to MLG, and won Blizzcon. We only hire the highest quality to ensure that your boost gets complete. That is how pvp and pve works on the site!