.22's are nice to have because they're cheap to shoot and a good training aid if you want to fire larger calibers. They're fine in and of themselves too, not just as a training gun for something larger. I don't necessarily agree that they are absolutely mandatory however. For children I'm more inclined to agree. Nobody would recommend a .22 for a concealed carry firearm.

Certainly, nobody should be asked to learn first time on a .357 snubby, but there's nothing wrong with learning using a fullsized Glock with standard pressure 9mm or a K or L-Frame S&W with standard pressure .38's. These are very mild to shoot and would serve fine as a first time gun for an adult IMHO. But full sized firearms are not generally the norm for concealed carry. Some do it, but most opt for something smaller and lighter. Smaller/lighter means more recoil, less controllability, and less accuracy (usually).

Once the new shooter learns the price of centerfire ammo, they'll probably make haste for a .22 or even a good quality airgun for cheaper practice.