Think it's both. Samsung does a guessing game and usually the more expensive phones don't sell as many. I mean look at the specs...$200 gets you 512 memory and 16 gigs ram. The ram really is Overkill, and for most the 128 memory is enough with SD CARD support $200 really isn't getting you much IMO.
I pre-ordered the Verizon variant ultra 512 from best buy, but have been second guessing that decision since preorder launch. With the shortages I'm seeing, I ordered a unlocked 128 ultra from Samsung yesterday. I'm expecting that best buy will be failing miserably on the ultra 512. I have both orders still active yet, I'll see how it goes next week, one will be getting returned or cancelled obviously. I'm not in a hurry to get it, but by no means I'm in the mood to deal with best buy and their 2 month later phone release. I am also interested in trying the unlocked version, I don't foresee me noticing much difference over the Verizon variant, we'll see.
Verizon is still showing the 128 available, I would probably go that route, chances are you won't get the promo waiting that long for the 512