I think they changed it because somebody did a miscalculation before releasing the game; according to official sources you were supposed to be able to get all possible endings in Single Player without ever starting multiplayer if you just was thorough enough, but it was actually just below possible (I think the maximum points you can get with a 50% readiness-rating is just below 4000 points).
Anyway, this is an even bigger reason to never choose Green
Edit: Anyone but me surprised at how easy it was to make peaceSpoilerbetween Quarians and Geth?