Unfortunately that's what the law requires. To gain protection over your IP you have to be vigilant and take prompt action or risk having the infringing party/parties use your inaction as a defense. So it's not so much that Apple is acting impulsively, they're merely complying with what the law expects from them. And, frankly, they're doing Samsung a favor because they're getting a legal ruling before Samsung's liability becomes potentially much larger (that's the basis of the argument for an injunction, that if it's not granted the damages will become too great). It does also serve as a deterrent to other potential infringers.
It's very easy to armchair quarterback these issues from a distance but it's far more complicated under the surface than a 2-paragraph summary in the news is able to explain.