I asked this same question years ago when I first got into handgun shooting, asked every gun shop owner "will the stainless model last longer than the blued one?" and most of the time they're like "If you shoot enough to worry about it, you might as well buy two of them"
It also all depends on the kind of stainless being used and the manufacturer. I HIGHLY doubt a company like Taurus is using the same grade of SS as Freeedom Arms. For $350 for a SS Taurus 85 or 82, the raw SS in that gun, if the same as an FA, would cost more than that before the gun was even forged.
People very knowledgeable on the subject say the stainless used in the .454 and .480 is heat treated differently and is a more expensive (better) stainless than the SS used in the .44 Magnum Redhawks and SRH's, and GP100's. The .44's and .357's don't need to be as "strong" for lack of a better word, than the .454's which have a lot more pressure and heat and thus the .44's can be offered at a slightly lower price. Bill Ruger was known for being frugal and there's no arguing that a SS Redhawk will last a lifetime or more......if more expensive SS isn't needed, then I guess pass the savings along to the customer.
There is also a lot of personal "preference" involved, there are S&W guys who will swear the carbon steel used in the blued and nickel guns is harder and stronger than the stainless. They claim the SS, especially in the early SS Smiths, is "softer" and the cylinder stop notches will peen faster and endshake will develop sooner. I'm sure modern SS alloys are better than those used in the 60's, for the first stainless S&W's. The .500 S&W is only offered in SS and there's no doubt that gun has got to be strong.
The FA revolvers had better be top grade stainless, to be chambered in stuff like 30-30 and 45-70
Like was said below, most of us will never see any real difference in durability in a carbon steel vs. stainless handgun. 99% of us won't be able to put enough rounds through it to see if a stainless gun will take more .357 over a blued one, maybe someone with deep pockets and a lot of free time will take a blue and SS GP100 and run 10's of thousands of rounds through them and report which one lasted longer
Rifles may be a different matter, since a barrel will wear out in 8-10,000 rounds in some cases...........but for guns like a GP100 or Redhawk......whether it's blue or stainless, good luck trying to wear one out.