The quick answer is.... Marketing.
When S&W introduced the .357 Magnum in the 1930s, they wanted a catchy name that differentiated it from its older parent, the .38 Special.
The .38 Special, developed in the 1890s, was actually a variation not on the existing .38 Smith & Wesson round, but on the then-military-standard .38 Long Colt.
The .38 Long Colt, when it was first introduced, actually DID use a true .38 caliber bullet, called a heeled bullet.
A heeled bullet looks, in profile, something like a mushroom, with a larger cap (which was .38 caliber), sitting on top of a smaller diameter shank, or heeled section. The heel fit inside the case mouth. When the bullet was seated, the outside diameter of the bullet and the outside diameter of the case were the same.
The heeled portion of the bullet was, .357 or so in diameter.
Starting sometime in the late 1880s many ammunition companies realized that the heeled bullet cartridge was hard to put together and had other disadvantages, such as the bullet lubricant being on the exterior of the bullet.
The decision was made to reduce the diameter of the bullets to a uniform diameter that matched the shank portion, in the case of the .38 Long Colt, that was .357, and in the case of many of the early .44s, such as the .44 Russian, that was .429.
The new bullet design had a lot of advantages, including lubrication grooves that could be seated inside the case mouth (making for much cleaner ammunition) as well as being easier overall to manufacture.
I've never found a good indication of whether the .38 Spl. was ever offered with heeled bullets, but I don't think that it was. I believe that it was one of the, if not the, first cartridges originally loaded with the new style bullet.
The only surviving members of the heeled bullet age are the .22s, Short, Long, & Long Rifle. If you pull a bullet out of a .22 Long rifle, you'll see very clearly what a heeled bullet looks like.
Finally, as for your question "are other cartridges named as loosely as this?"
The answer to that can best be summed up with...
"Oh my God, practically all of them!"