Yes I noticed that too. I'm not sure why they gave it a different name.
A lot of class specific feats are now in various APG archetypes. From every class. Look around. That is the plan.
Is this something paizo is planning to continue? are the AP special 20th level feats supposed to act as a testing-ground of stuff thats gonna become common in future books?
That... Actually makes a lot of sense. Both from a game design standpoint and from a world lore standpoint.
Mechanically, if they introduce some powerful ability as an uncommon option in an APG and it is horribly and unexpectedly broken - they can avoid putting it in as a common and universal option.
From the lore, if the barbarians of this one area are wrecking face with this cool, powerful ability - it makes sense that the ability is going to be reverse-engineered, emulated, or outright stolen by barbarians of other areas of Golarian.
Aside from a slightly different flavor description and the fact that Invulnerable Juggernaut is uncommon, these feats are exactly the same.
The same thing happened for fighters and wizards, except they kept the original name of the feat.
As you and breihauptclan surmised, the Adventure Paths and other supplements gives Paizo a chance to try out stuff without upsetting the whole game, since it's all "locked" behind a noncommon rarity.
It wouldn't surprise me if some of the stuff from Lost Omens: Legends will eventually make its way to a core book.