This obviously did not apply to the Christmas Tree in "The Christmas Invasion" but we'll have to call that the exception that proves the rule.
Cos they only move when they are not observed, even when you blink they will move. And they are very fast. They can move miles in one eyeblink. Also because they look scary with their vampire teeths. When they look normal they still scary. The worst face of an angel is the face from the clip in "The Time of Angels".