I think it comes down to this:

The FBI will get into the phone. That's never really been at issue. The question at hand is how easily they will get into the phone, and what that means for device manufacturers moving forward.

the FBI is arguing that they can compel Apple to cripple encryption after the fact. Apple is arguing they can't. It's a hell of a precedent to set, and most manufacturers have been trying hard not to set it. American manufacturers are already hindered by laws against strong encryption in the United States; it doesn't effectively keep Americans from using them, but it does keep American manufacturers from selling them, giving European and Asian vendors a leg up. Aside from issues of civil liberties (which I in no way mean to discount), giving American law enforcement agencies the precedent of cracking into any American device however they want whenever they want because they decide they should is likely to have a chilling global effect on American technology companies.

And the thing of it is, weak encryption is adequate for most people. They're not looking to protect their information from the NSA, they're trying to keep their credit card info safe from their children. They want to know that if they drop their phone on the street, they have a few hours to wipe it remotely before someone hooks up a dongle to it to brute-force the combo. The type of encryption and the methods of decrypting it aren't really at issue.

It comes down to the government wanting the legal right to compel companies to disable their security features whenever the government says so and Apple, in this case, arguing that complying with the government would be bad for their customers and bad for their bottom line.

And I suspect that Apple will win.