It seems to depend on the program. cat is very quick to respond to ^C whereas in vim, less and elinks often a large amount of text is printed before ^C is echoe

It seems to depend on the program. cat is very quick to respond to ^C whereas in vim, less and elinks often a large amount of text is printed before ^C is echoed and takes effect, like you describe. I suppose that has to do with the size of chunks written. In reality though it's more about the trickling than actually mimicking a proper serial connection.