The real differences outside of cantilever mass and stylus differences probably are limited to the quality of the winding in the pickup and the suspension on the cantilever. That can make for a significant difference though, so just because the basic technology is the same on all mag cartridges they can certainly perform differently. Of course the stylus plays into it majorly too, which is why the same body will act different depending on the nail installed.
Kind of like the differences in audio output transformers. On the surface they are all two coils of wire next to each other inside an iron frame. Internally they perform very differently based on precisely how they are wound.
