The answer is stiffness.

You want the mainbeam setup to be very stiff in the vertical plane. The more material in the dolphinstriker the stiffer the mainbeam setup. You can get alot more material (stiffness) in say 30x3 SS strip then a 7 mm ss rod. About 2.34 times as much. 7 mm SS wire is less stiff then a 7 mm rod, so you loose even more here.

Additionally there is hardly any difference in tension resistance between a round second and a flat rectangular one. Also it is alot easier to fit a flat strip to the underside of the mainbeam then a round rod; same for fitting the dolphinstriker pin to the strap. It is easier to bend a flat strip into a V-ed shape then a thick round rod and last but not least a frontal area of 3mm by 1500 mm is significantly less then 7 mm by 1500 mm when impacting with 1000 kg/m3 water. And and I forget that a flat strip keeps the pin in place in the horizontal plane were the rod and wires will do so muhc less. In fact the pin on my boat is not even secured in the beam. It was just slid in and there is no hole in the strap either, just a piece of metal welded horizontally to the end of the pin adjustement threading. This T-ending actually secures the pin to the strap and when under tension it can not move at all. Best part is that this setup can be taken apart in mere seconds and I have done so. Just turn the screw to detension the pin, move the T-ending up and turn it through 90 degress, angle the pin and slide the whole thing out of the beam.

In fact there is no good scientific reason to use round rods; only guts feelings to that extent.

Wouter