Visual feedback needs to serve a purpose. This is a stop watch we're talking about - one that shows time in tens of milliseconds, which is less than one frame interval at 60fps. Any animation done would hinder the function of the stop watch and raise ambiguity about when the stop watch actually started and stopped. So not using an animation is the right thing to do here. If they'd gone for consistency in this case, it would've been "foolish consistency" [1].
[1] "A foolish consistency is the hobgoblin of little minds." - Ralph Waldo Emerson
edit: typo fix.