spamc/spamd certainly are command line tools, but isn't everything?

No. The interface from postfix to amavis and back is SMTP. No launching and unlaunching. In fact, the interface to amavis is something else (LMTP?) that both postfix and amavis understand that permits individual senders to be accepted/rejected, even though only one copy of the message goes forward.

It's all incredibly slick. I'm really happy with it.