Think of how famous people from different eras would react with one another... and who's to say that you would be in the mood to have dinner with all of them at once-unless it was to sit back and watch the interplay among people who wouldn't have been able to meet together in their life time (or if they did, you weren't there!).
Some answers to this question have been flip and others (dare I say) sound like they were either composed by publicists or they've been asked so many times that the interview subject has a ready pat answer.
And what kind of dinner would it be? Politesse or bon homie?
And a dinner, say, in London or Malibu or Paris or Silver Lake would each be different... no?