A sculpted neck does not 'cut the articulation' as you say. Most of the articulated joints already exist on the Buck. The head-neck joint is just one of many modifications found on the Prometheus. The major improvements of the Prometheus are found in an increased ROM and smoothness of the joints (neck-torso, mid-torso, and elbow joints especially), along with better limb proportions, and hand/foot connections.
A number of members on this board have expressed their preference for a sculpted neck because of details like the Adam's apple and beard stubble. Even today, in the Indy thread, people are getting excited at the proposition of Darren adding a sculpted neck to Indy. Well before the Prometheus was announced, I advocated the best of both worlds: a sculpted neck piece separate from the head.
Hot Toys has made the True Type body for a couple of years now. Why would they still be making heads like the Joker with necks that fit onto an adapter? It is possible that the artist prefers the look of a sculpted neck versus the generic one.