Can you explain what does? I don't think that I understand what you mean.
It doesn't need to be, does it? As I have twice stated, I referred to cartridges in the .45 ACP / 15,000 PSI range, not the .357 magnum / .44 magnum / 35,000 PSI range.
A product-improved Webley that uses modern metallurgy and modern lockworks (say from a Ruger Security Six) would last through many, many rounds of 15,000 PSI ammunition.
I don't think anyone has bothered to actually try explaining this yet, so I will give it a shot...
Chamber pressure is (mostly) contained by the chamber, in this case contained in the cylinder.
The rearward load that the frame takes is the recoil from the case head against the recoil shield (which is partly from the pressure of the combustion of the propellant, but just think of it as the recoil, because the pressure is just part of it).
The forward load taken by the frame is from the friction (not actually just friction, but think of it that way) of the bullet traveling through the forcing cone and the bullet. The bullet "wants" to take the barrel with it. So, this is determined not by the pressure behind the bullet; but things like the frictional coefficient of the bullet material (which is why Buffalo Bore likes to use hard cast projectiles, lead is more slippery than copper), the length of the bearing surface of the bullet, the velocity of the bullet, twist rate of the rifling, and probably some other things that escape my mind at the moment.
Recoil pushes the back half of the frame backward, while the bullet friction (again, just think of it as friction) pulls the front half of the frame forward, stressing the latch at the top/rear and the hinge at the bottom/front of the cylinder window. We need to get away from saying that a solid frame is "inherently" stronger than a top break without adding qualifications, because you can make a top break just as strong as a solid frame, it just takes more mass. If we were building solid frame revolvers out of cast aluminum and top breaks out of tool steel, that also wouldn't be a fair argument. If we keep the materials the same, the mass required to build a top break of equivalent strength to a well-designed solid frame is going to be more.
Pressure isn't what you are fighting, which is why it has been shown to be possible to make a .357 mag top break. At least it is rumored to be extant, but I've never seen one. Look up the MP-412 Rex. Also, .22 LR as we've seen in the Iver Johnson sealed-8 and the H&R 999 is higher pressure than .45 Colt, if memory serves.
Ultimately what you are fighting is cost of manufacture. It can be done, but it will never be done in the same way as the turn of the 20th century, because .38 S&W is no longer acceptable. Yes, .38 S&W is low pressure, but it is also low velocity and recoil. There are also issues with case length (you've gotta cam the extractor longer) adding to cost of development and manufacture. If you make a steeper cam, you'r extraction is not going to be as easy, so you need to toughen up your camming surfaces, polish the chamber(s) as much as possible, etc.
Clear as mud?