1) It wasn't a canary to begin with, so its removal means nothing.
2) There's no legal precedent for disclosing a Section 215 order by killing the canary, so Apple removed it before they received a Section 215 order. That way it doesn't disclose anything and Apple avoids legal liability.
3) Apple really did receive a Section 215 order.
Killing the canary does actually reveal the order, which violates at least the spirit of Section 215. Under the wrong circumstances, that could get you jail time.
On the other hand, making materially false statements after Sarbanes-Oxley can also get you jail time.
So yes, Apple could have realized that they had painted themselves into a corner that they really didn't want to be in. Having said all that, though, my money's still on 3).
Of course there's question as to whether the spirit of Section 215 is constitutional. It may be reasonable for the government to force you no to say something.
But can the government force you to knowingly make a false statement?
I'm inclined to doubt that they can. But they can keep you locked up for a decade while the case makes its' way to the Supreme Court.
There are no checks against their power-- no court, no congressional group, and no group of people is willing to regulate the "watchmen".
This is the default state of affairs, and it only changes when there is strong public outrage and pressure for the government to do their damn job of watching over the watchmen. Which is seriously screwed up.
No, but they can punish you for telling the truth. The fact that you'll be punished for lying does not negate the punishment for telling the truth, just as the fact that you'll be punished for telling the truth does not give you an excuse to lie.
So yes, if you are in a circumstance where pleading the 5th is allowed, then you may plead the 5th and therefore not comment. But in the case of a corporation, or in the case of circumstances where you may not plead the 5th, then you cannot escape punishment by asserting that you are in a catch-22.
The page that states this is http://lawcomic.net/guide/?p=2600, though the next couple of pages are relevant as well.