why, why EPCC
I'm not Erik, but I've got a feeling there's a quite a few reasons. The first obvious one I can think of is the custom tuckcase. I'm not sure if that's possible with USPCC or the potential cost of it. I believe the custom tucks that have USPCC decks recently (Independence LTD, D&D Private Reserve[?], etc) have to be sourced out elsewhere so that one had to co-ordinate the deck printing and tuck printing/manufacturing. I'm sure it'd be easier if one factory could do it all. And the vertical cigarette inspired tuckcase for the Mana decks do look really nice.
I've found that EPCC tends to be better for registration for thinner borders from the decks I've purchased. More consistent when you riffle shuffle them that it's harder to notice.
I'm curious to see which court card set Erik will use to go with the Sybil decks, but it's look really great.