Hi Skepticon,
I was wondering the same as you.
After reading the page a few time, the only thing I can think about it’s they charge for a pet and wings that are include in the Prime Evil Collection (in addition to Diablo 2 Ressurected and Diablo III Eternal collection)
At the end of the page, last bloc in the “Defeat Evil at its Prime” section
Bend Hatred to Your Will
The Diablo® Prime Evil Collection also includes the Mephisto pet and the fearsome wings, Hatred’s Grasp, for Diablo III. Fight the denizens of the Burning Hells in style and be the envy of your party wherever you go.