And as @chiph says, the canary doesn't really have to die after a secret warrant is served, it just needs to sing a different song: "Your data has not been disclosed to law enforcement for [ 179 ] days".
A startup that's trying to get some notoriety in a few months or even years can definitely do something like this. Apple, who has to plan on a longer time horizon and who probably enlists the soft power of the government on a regular basis, has to be more cautious.
I can hire a team of lawyers and finance people to set up a complex system of subsidiaries so that my company only realizes profit in a specific way in a specific jurisdiction to avoid taxes, and as long as we've all followed the letter of the law, there doesn't seem to be any problem with the 'spirit of the law'. In fact, entire companies of accountants, lawyers and business consultants exist solely to help other companies follow the letter of the law while avoiding the spirit of it.
What makes it so that laws regarding anything "tech" get to be written and interpreted so vaguely and widely (from warrant canaries to copyright issues etc) when rules for everything from finance to oil spills are narrowly defined and interpreted?
Luckily, in the US at least, it's possible for a few nerds to build a company (say, Dropbox) that's as financially valuable as some long-established government schmoozers but has never thought about regulatory issues. So the "young" tech companies like Microsoft, Apple, Google, Facebook, etc. are less capable lobbyists on average.
When cars were first introduced, many towns across the UK viewed them as an opportunity to make money by fining the rich by setting obscenely low speed limits (think <20mph) with extraordinarily high fines. In response to this, the AA was formed to warn motorists of speed traps down the road.
This started to cut into profits, so the the government retaliated by charging and convicting an AA guy with "obstruction of justice". AA agents were therefore not allowed to inform motorists of speed traps.
The AA responded by changing their protocol. They would always salute passing motorists unless there was something wrong (aka, unless there was a speed trap). The absence of a salute indicated a speed trap, and the law could not force the AA to salute.
I'm not sure if this was ever challenged in court, but they were able to keep it up for several decades so it was never successfully challenged in court at least.
Edit: The AA could be considered sort of similar to the american AAA ("triple-A"). http://en.wikipedia.org/wiki/The_Automobile_Association http://www.theaa.com/aboutaa/history.html#tabview=tab1
And what kind of free society can force citizens to salute? "The government won't tolerate warrant canaries" makes intuitive sense because we have grown used to the courts throwing out all sensibility whenever there are computers involved, but the idea of the government compelling civilians to salute "in meatspace" seems blatantly beyond the pale.