How booze entered the picture, i do not know. Last I knew, it wasn't particularly salty. Liquid, yes. Salty, no.
Vinegar was a common alternative to salt for preserving foods...
With today's freezers, heat treatments and hermetic sealing of containers, there is little actual need for pickling, but it is still quite common, because people have become familiar with and desirous of the flavors generated by the process. I believe that today, most Americans do not think of salt when they think of pickling. Sauerkraut, some fish (cod, salmon) and pork (in some areas of the country) are still salt-cured, but most "pickled" products today are processed in a mix of vinegar, salt, and pickling spices. Both the salt and vinegar content of today's more common "pickled" goods (and I mean commercial products) have been reduced to such a degree that a jar of pickles bears the warning "refrigerate after opening."
Also, I've only heard of "souse" as boiled, chopped, and pickled secondary meats, usually but not always bound in gelatin. I've looked briefly on the internet and found no "souse" recipes but for this kind of souse. I'd like to see the kind of salt-cured recipes Slava has mentioned, because I'm a flavor craver, and I'm always looking for different foods to try.