Bob, I was a mechanical designer for part of my business career, but certainly not an engineer.
You, and the Rifleman's staff, are correct about the arrangement of the Webley's stirrup latch, and I was wrong. I had forgotten about the recesses in the pistol's frame, and I mis-remembered the number of screws involved.
Nevertheless, I am not willing to concede that the stirrup-latch idea is mechanically strong. It is sufficient to restrain the relatively weak 0.455 round (and, through pistol modification, .45 ACP), but that's about it. I don't believe that it could be modified, or strengthened enough, to contain a higher-powered cartridge, for instance .357 Magnum, .44 Special (Keith load?), or .44 Magnum. I am not certain that it could be built to regularly withstand even .38 Special.
Years ago, I toyed with a top-break design that would place its latch in compression, rather than shear. I thought that it was a good idea for the same reasons that you do, so I took it to a real engineer who was familiar with metallurgy and manufacturing processes.
He shot me down. Although my compression-stress idea was a good one, the real difficulty was in the complexity of the forms, and in the way the mechanism had to fit together. It would've been very expensive to produce, even in large quantity.
I believe that this is the reason why we do not see further development of the top-break idea.