You're stating it wrong. When someone is dead you can say what you want about them.
No, you are over simplifying it.
The actionability of the utterance usually depends on when it was said... and as the Jesse Ventura vs Chris Kyle case so recently demonstrated, a dead man's estate can still be on the hook for damages. Had Ventura died first the case still could have proceeded provided the claim was made prior to death (and likely the suit as well).
Defamation aside, without a conviction or lengthy civil suit, the rights of the estate to the properties of the deceased/accused/etc does not end as it would with a conviction which goes to the heart of what I said above.