I stock food and follow this procedure, but can see that these are not only the same family - the gourd family, but also the same species.
Both have a hard outer shell. Why does one ( Zucchini ) require refrigeration but not the others?
I would assume the answer holds true for cucumbers as well.
The short answer is that they are different types of squash, although both are squash.
Zucchini is a summer squash, which has soft flesh and a malleable rind.
Both acorn and spaghetti squash, much like pumpkins, are winter squash, with harder flesh and a tough rind. If cured, they can be stored for months at cool root cellar temperatures, and for a reasonable amount of time at regular room temperature.
I'm pretty sure they're not the same specie, as for your question, it's because zucchini is a summer squash and spaghetti and acorn squash are winter squashes, which has thinker rinds which insulates them
