"s intact; why does
2ci" (and the same formula with any higher number) delete them?
I suggest you read doc/motion.txt. It states that with count 2 the quotes are included and thus i" works a bit like a" except no extra whitespace is added.
EDIT: Just to be clear, I don't strictly speaking provide an answer. I take this behaviour as the design decision of the author and since he did not provide rationale in the manual, you can only ask him, why he decided to do this and not something completely different.
First, you need to know what
ci" mean in
"means double quote literal text object.
change a string inside quotes. Adding
2 applied change command over