Well, I've never been invited. And I suspect it's for one of these reasons:
(1) The client couldn't stand the sight of me when it was finally over (I've found that when I send a former client a simple holiday greeting, they groan and wonder what bad thing has happened- me and bad memories, we go hand-in-hand); or
(2) The party never happened - the client realized the divorce was too sad, too anti-climactic or too damn debilitating to leave much energy (or much money) for celebration.
I've seen a few photos of "divorce cakes" on the Internet (seems like they're more pro-women). I wonder if they're for real and if they are, how many people actually enjoy eating them.