dontomasso's got it right. Frankie's immediate response to Tom is to close all loopholes; so the first thing he says is, Yeah - but only the big shots, Tom (the actual dialogue uses the words "rich guys"). He then goes on to say, "The little guys -- they got knocked off and all their estates went to the Emperors. Unless they went home and uh, killed themselves -- then nothing happened." Only after that does he utter the sentence, "And their families -- their families were taken care of, Tom."

The main thrust is that, while Tom speaks obliquely, saying how the Corleones were like the Roman Empire and what happened when a plot against the Emperor failed, Frankie exhibits more courage and turns the conversation to the realities that must be faced: Yeah, I know about the Roman Empire, and the automatic protection for the rich guys. But to Michael Corleone, I'm a little guy... and I know what's required of little guys. It's as if Frankie was voicing the part of the conversation that Tom wasn't yet able to express, which adds to the scene's poignancy.