It's not about the shape (well aslo about that, though), it's about the make and hence for durability.
Shaping the breast pocket to some curved thingy by mainly manipulating it with an iron takes a fraction of the time than getting the rounded thingy-shape shape by cutting, sewing etc.
I thought you guys were always so anal about that stuff
The shape is cut and sewn, there is no stretching when you make this breast pocket. "ye olde Rubinacci" is a bit more authentic as the front edge ( towards the lapel) is at an angle and not perpendicular to the sewn edge at the bottom giving more of the expression of a Spanish Galleon. (common sighting in my day). This point is more vertical on the others. The missing feature on all these is that a proper execution of the barchetta has swelled edges in the space between the stitching and the outside edges. The Rubinacci may have had this and it has suppressed over time.
Well, there is a bit of stretching but it is the cloth that is folded over the top edge of pocket. Since the pocket top edge is curved the folded over cloth is strteched to sort of fan out on the inside/backside of the pocket. There is no stretching on the face of the pocket. That's a silly notion, stretching with an iron would distort the lines of any pattern in the cloth and the pocket would not look pretty.
Well, it's a barchetta, but one that is sinking (like most), put it that way.
Of course it is always cut and sewn, but most companies get in the lion's share shape by ironing (sorry Despos, the same is the case for curverd patch pockets) and sometimes by a difference in height between the left and the right edge of the breast pocket welt (as cutting and sewing a perfectly even, real curve is not that easy...I mean if it was, why didnt they just do it for all of these barchettas one sees today?).
It is is easier and less time consuming than starting with the premise of making a perfectly even curve at the bottom and exact same width at the edges by cutting and sweing alone.
Both are not superb IMHO, the left one is pretty straight at the bottom and from the middle the "curve" is a straight line pointing upwards, the edges are also obviously of quite a different width.
It lies flat on the chest (what I would consider as an objective construction mistake, when the curved welt lies flat on the chest when the jacket liies flat it will not adjust perfectly to the shape of the chest when worn), the one on the right is pretty straight and and at one point suddenly jumps into a curve.
Thanks for the attention and waisting your lifetime reading about ulgy curved breast pockets.