True, the scenario in which ctrl+alt+del would help is one in which only a limited account had been compromised, but the SYSTEM level winlogon keylogger allows

True, the scenario in which ctrl+alt+del would help is one in which only a limited account had been compromised, but the SYSTEM level winlogon keylogger allows you to do things like turn local admin into network admin and it certainly doesn't require kernel mode access. I was more commenting on the requirement of kernel mode access or hijacking of special interrupts than on the usefulness in general.