Well, there's a LITTLE more to it than that! It seems that the main attraction of the .40 S&W round is that it can be chambered in handguns of small size, equivalent to those shooting the 9x19mm. This permits carrying of a more powerful round without having to carry a bigger gun! (By whatever measure you choose, whether momentum, kinetic energy, frontal area, permanent wound cavitation volume, etc, the "best" .40 S&W loads outperform the "best" 9mm loads.) Sure, the purveyors of the cartridge/guns want to make money, but the products are attractive to the customers, as well, and for a justifiable reason.
Personally, I don't particularly like the .40 S&W cartridge, since in my hands at least, it's less accurate than the .45acp or the 9mm. Most handgun cartridges fill a niche of some sort, however, and the .40 S&W's appears to be "size-efficiency", Mark Moritz' term for the appropriate correspondence between handgun size and the power of the cartridge fired by the gun.
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"Potius sero quam nunquam."