I always wondered whether that was all the Daleks in the fleet at the end of the last season, if the Doctor had already nearly completely wiped them out once, wouldn't it make sense, once there was a lot of them, for them to split up, rather than all remaining in one place.
Did all of the Daleks and Time Lords fight in the Time War, didn't they think what might happen if they lost, or did both sides see it as all or nothing.