I guess nothing on Person of Interest is true...
I do though think Apple holds the "key" to unlock these devices and I also think that if someone is suspected of a violent crime or act of terror they should have to relinquish their property, in a state that the information can be accessed. Opinions otherwise are skewed because they currently aren't the victim and until they are, those views will not change.
Here's the long story:
There _is_ software on your iPhone, created by Apple, that can unlock your phone. That's the software that runs when you enter your passcode. You enter 1234. The software tries to unlock the phone with the code 1234. Obviously that will only work if the code _is_ 1234. The unlocking has been cleverly designed so that it only works on that iPhone (you can't use some supercomputer to do it, you _need_ the locked iPhone), and it takes about 0.1 seconds. It can't be done faster. The unlocking software on your phone has some tricks: For example, it can be set up to erase your phone after ten failed attempts. That's why the police can't unlock your phone by just typing in 10,000 passcodes.
If that software can unlock an iPhone, why can't some other software do it? That's because it requires some hardware in the phone, and the hardware requires that the software is signed by Apple. You and I can't write software that unlocks an iPhone. Well, we could write it, but it won't work if it is not signed by Apple.
Apple has software for iOS7 that can unlock a phone without the limitations of the normal unlocking software. That software will just try one key after the other. A four digit passcode has 10,000 possibilities. Each attempt takes 0.1 seconds. That's 10,000 times 0.1 seconds or about 20 minutes. But if you have an 8 digit passcode, that would mean about four months. If you have 8 letters, it's uncrackable.
That software is rejected by iOS8 (intentionally) and Apple isn't creating a new version that runs on iOS8 or iOS9. So Apple doesn't have the software that could unlock your phone by trying all passcodes. Apple _could_ create such software but refuses to do so (for good reason), and nobody can force them to do it.
In the future, Apple could probably change their hardware so that any limitations (like destroying the data after ten wrong attempts) are enforced by the hardware, so that Apple _couldn't_ unlock your phone with brute force.