Actually, you are being a little silly or at least naive.
Lots of gun manufacturers offer multiple calibers within a specific model. For instance, you can get a Remington 870 pump shotgun in 12 gauge, 20 gauge, etc. and a Winchester model 70 rifle in dozens of calibers. Its like cars models having multiple engine options. Some companies, Glock for example, give each caliber a different model number though. Your Smith and Wesson and mine are apparently the same model, but different calibers. This was my dad's gun, which I inherited, and he chose .357 Mag as opposed to .44 Mag.