I've found that the best sys-admins know enough programming to automate their jobs and debug application issues. They don't have to be the greatest programmers, but they're fantastic debuggers.

The best programmers know all the system settings, services, and behaviors that can affect their apps and thus have to know the underlying system.

I have yet to meet a truly great programmer who didn't thoroughly understand the system he was running, or a fantastic sys-admin who wasn't a pretty good programmer.