Since the question was "Ctrl-z works universally", I feel obliged to point out that ctrl-z sends SIGTSTP, which can be blocked--not to be confused with SIGSTOP, which cannot be blocked. I don't know of any program that does intercept SIGTSTP (except a test program I wrote that tries to print the name of any signal it receives), and I suspect that "polite" interception would be to release a few resources and then accept being paused--but, in theory, a program could ignore it.