Could be "photo illusion" but the head design on these new Braun shavers looks slight rounded to the convex vs their old heads being more flat. I wonder if that is what helps catch those flat hairs.
The Arc 5 really is convex (hence the "Arc" I presume), but just checked and the 73s head on the new Series 7 seems to be perfectly flat. The center cutter bar does have a different pattern than the older 7 or the Series 9, so that may account for the difference, but it does seem to me that it picks up flat-lying hairs better - again, some disagree.