Apple's not going to sue itself. So they can of course unlock their own phones (barring a contractual restriction with AT&T or similar).
The change means that, i.e., Google, or TMobile, or some other legitimate competitor to Apple could use jailbreaking or unlocking as a competitive strategy in a way that Apple wouldn't like. For instance, Google could operate their own app store, and consumers could use Google software to unlock their device and install Google's app store.
While Apple does offer unlocked phones in some countries, they typically don't do so willingly. All of the unlocked phones that I am aware of come from countries that forbid locked phones to be sold.