...I might add that no, Ruger pistols are not more durable then any other either, they contain cheap mim component parts and generally break at greater frequency then any top tier pistol.
I don't have much experience with the newer Ruger products, but the old P-Series guns were very durable. Some years back I talked with the owner of one of the largest rental ranges in the DFW area and he stated that the Ruger P-Series autopistols were the most durable guns he rented.
The reality behind this is simple, forgings are stronger and more durable then castings.
Well, all else being equal (which it almost never is), this is probably true.
You have to hold everything equal to be able to make the statement about forgings and castings. A good quality casting can be stronger and more durable than an identical dimensioned poor quality forging. A casting that is well-designed for the application can be stronger and more durable than a forging with a poor design or a design flaw. A casting that contains more material can be stronger and more durable than a forging with less material. A casting made of a superior strength alloy can be stronger and more durable than an otherwise identical forging with a lower strength alloy. And so on and so forth. The simple reality is that reality isn't simple enough to be able to make sweeping statements like "forgings are stronger and more durable than castings". You need to have access to a lot more information to be able to compare the strength of two different parts--simply knowing that one is cast and the other is forged really doesn't tell you anything at all.
Anyway, the old Ruger was pretty good about making sure that they used enough material with the proper qualities, of the proper quality, and shaped properly to make strong durable designs regardless of the methods used to make them.
I'm not arguing that the P89 is a superior gun to the Beretta 92--I don't think it is. But the P89 is not lacking in the durability department. In fact, just the opposite is true--it's a very strong and durable handgun.
Ruger would not have taken the hit to its reputation when they discovered it was not strong enough to be re-chambered into a .44 mag, as the S&W 686 was, or the latter 669 is, instead Ruger was forced to chamber it in .44 spl which absolutely nobody wanted, especially when you can get a .44 mag for same price.
Not that it's especially relevant to a discussion about Beretta and Ruger autopistols, I suspect that the decision was not nearly so much about overall strength as much as it was that the GP100 design resulted in a much thinner forcing cone when converted to .44 than was the case in the L-Frame adaptation.