All we know is what they do. It's not a stretch by any means to suspect that when an American corporation adopts uncharacteristic policies that violate their customers' privacy, the government is probably involved. Difference here is that unlike TrueCrypt, Apple can't just shut down. Hell, even the rumor of Apple doing this has beneficial impact to law enforcement. The press release may be the product.
Let's take the effort at the most altruistic face value - defeating child porn mongers. If you're trying to herd such people to a very narrow set of solutions that you can monitor and/or control, simply undermining trust in the alternative options may be enough without actually implementing invasive tools being discussed. The comedy in some of this is how hammy the next act can get - if I were a cynical man, I'd expect a technology to come out in response to Apple's move, or maybe it's out there already but suddenly gets a new push for mindshare. I'm sure the security world has a term for solutions like this. Not really honey pots, but more like fly paper. A product the agencies have either straight up owned or surreptitiously gained control over, marketed to people who would use it for ill.
So, how can Apple make any argument when they legally aren't allowed to talk about it? Do you think Cook believes in your privacy so much he will go to prison for revealing it? Nope, he's the one who let them in Apple to begin with and "privacy" is a sales pitch everyone laps up. They've been compromised for over a decade. There is no security. It's all lies on top of lies. Have you ever heard of what happens to people when they reveal top secret government spying programs? Snowden? Drake? Binney? Manning?
I'm just some guy with a beard, I honestly don't know anything about anything- in my eyes, it looks like less of a legal requirement and more of a stepping stone. Granted, those things aren't mutually exclusive and I'm not privy to any information others don't have, I'm just cynical.