Something Defoe said made me think about this, he said 'we all have to do it' (or something like that) referring to turf.
This is interesting because my son used to play only on turf summer and winter, and when tournaments were held at his home field the home teams would nearly never lose, I know that this is likely because the ball bounces and rolls differently on turf.
Half your games are home games and most other teams don't have turf so this would lead me to think that teams like Seattle would have a greater advantage when playing at home.