I really don't know why BitMain moved away from the the controller board they used in the S1 and S3 (well I guess I do...the answer is cost).
Old board was less powerful than new one, and this architecture is quicker to program.
Less powerful in what way? I still say it would be nice if bitmain offered a wifi option, even if they charged a few bucks more. Maybe others could weigh in to let bitmain know whether or not they would be interested as well?
In my case the "bridge" option described by bitmain, is more trouble than it is worth. Maybe when I decide to upgrade my whole wireless network I will give the bridge idea another shot.