...on related note, any reason why don't just list every quake sound & model in the worldspawn in order to avoid precache errors?

There's a limit on how many models total you can have precached. In vanilla quake the limit is 254. And every time you add a brush entity to a map, that also consumes a precache slot. In a sense, every model you precache needlessly is one fewer brush model your map makers can use.

Of course, it's worth understanding that Quake is a 1996 game. Computers of that era didn't have the memory to precache all the models - if you look at the original ID1 maps you'll notice that they never have more than 6 or 7 types of monster in a level. This was undoubtedly a concession to memory pressure. More modern engines raise the limit, but they did have to introduce new network protocols to do so - it wasn't a trivial change.

This kind of thing probably applies to sounds as well, but the pressure is a lot lower there. While a map will routinely include a small or medium number of custom brush models, it's rare for it to introduce a single custom sound (the basic Quake mod has no facility for this, it's only possible if your mod adds it).