They can, they should, and they must. They have a legal obligation to maximize profits.
That statement sounds like it came from somebody who learned about business laws from reading Cryptonomicon.
If only "maximizing profits" was such a simple formula, we wouldn't need all these expensive boards of directors and CEOs to run companies. Unfortunately, it's rarely clear what actions lead to increasing profits, and it's even less clear what "maximum" profits are. It's not even clear how far in the future are we need to look for our estimates!
A board can look at opinion polls, and determine that trying to ban a competing product will destroy enough of the consumer goodwill that it's not worth it in the long run, especially since the next-gen Samsung product would come out shortly after. That same board might decide that trying to ban a competing product will create short-term spike in that product's sales, hurting their at the time when they are about to launch a new product of their own. Considering that such an attempt might even fail to produce the ban, the overall result might be quite detrimental to their profits.
It's really not clear at all, in my opinion, that attempting to ban Galaxy SIII is in the best interest of Apple shareholders. So, to respond to your statement -- "they can" -- yes, "they should" -- matter of opinon, "they must" -- certainly untrue.