Exactly. If they really couldn't break it, the last thing the FBI director would be telling the public is "Hey, here's a device that criminals could use and completely cover their tracks!" By persuading the public that these phones provide an impenetrable wall that law enforcement can't get past, they are hoping criminals will feel comfortable recording their secret activities on their phones. This could provide a treasure trove of information and evidence for law enforcement.
No matter how strong the encryption algorithms are themselves, there's nothing to stop the FBI from planting a malicious app (a keylogger for instance). They could even serve Apple with a warrant to require them to install this app as a software update. And there's nothing to stop them from serving a warrant to the user of the phone him or herself requiring them to unlock the device. And, of course, there's always the possibility of exploiting vulnerabilities in the OS or some poorly written app. It's hard to believe that the iOS operating system has perfect security.
So it seems pretty clear that this publicity campaign is really all about creating a false sense of security. Think about it: if the FBI were really concerned, they'd be having quiet discussions with Apple, not shouting their concerns to the public. Is anyone not going to buy the device because the encryption is to strong for the FBI's taste? So what would the purpose of this publicity campaign be?