It's not just a bad hyperbole, it's a terrible cliche. Rugers built like tanks, Pythons delicate, and Model 19's not built for a "steady diet" of hot magnums. None of it is correct, but the fact that these sayings are all wrong, hackneyed and trite doesn't stop them from being repeated ad nauseam.
The frame does not contain pressure per se, but it does see stress from the pressure. When the bullet is still in the cylinder, the frame mostly sees stress from recoil. Once the bullet leaves the cylinder and enters the barrel, there is pressure that is forcing the cylinder back away from the barrel. The gap relieves some of this pressure, but it does not relieve it all or barrel length would not affect velocity. So long as there is pressure in the barrel behind the bullet, that same pressure is trying to blow the cylinder off the back of the barrel. The frame is the thing holding the cylinder to the barrel.
There has not been a steel revolver model made by Colt, S&W or Ruger that was insufficiently strong for many tens of thousands of firings of the cartridge for which it was designed. There are wear items like cylinder stops, notches, and the hand which wear on all revolvers. These are small metal pieces that rotate the cylinder and stop the cylinder's rotation. The greater the mass and diameter of the cylinder and that faster it is accelerated by the shooter's finger, the greater impacts these parts will see. These parts follow the original design by Colt on virtually all revolvers made by anyone, but the cylinder mass and diameter, and the size and material of the hands and stops vary with different models.
The SP101 has a small diameter 5-shot cylinder that puts less stress on the hand to rotate it and less stress on the stop and notches to stop it than a large steel 8-shot N-frame cylinder. You can get a Titanium N frame cylinder to help mitigate that stress, or shoot slower. In my mind, the SP is not a very clever design. Kimber and S&W have made revolvers that do everything better (lighter, smaller, more rounds). Lauding the SP for unnecessary strength or durability doesn't commend it to me. It's built like an anvil or a boat anchor. How is that better for me in any practical sense?