After doing a little more digging, this is what I've come up with.
There is the old / discontinued Field and Sport (Discontinued in Dec) that doesn't have the upgraded arms or the 800 / 1000 grit stones still being sold for $299.
The "new" Field and Sport comes with the upgraded arms but not the 800 / 1000 grit stones and it is also $299.
There is a Field and Sport Pro that has the upgraded arms and includes the 800 / 1000 grit stones being sold for $450.
There is a '"newer" version of the Field and Sport Pro called the Field and Sport Plus - it's the same as the old Pro model but being sold for $369 by only one retailer that I can find. If you google Wicked Edge Field and Sport Plus you'll find it. It's not available yet, they're calling for mid August before it's in.
Why all the changes?
The Wicked Edge 3rd Generation is coming out.
So, having said all that, I think that's why there's a difference with the upgraded arms on the "new" Field and Sport for the same price as the old one.