Dear Jansy,
it seems to me that Nabokov might mean merely that the idea of an Atheist dying happily
in his own bed is "against all rules" (for an Amercian novel) - he discusses this himself
somewhere -doesn't he?
And Pushkin means simply that he doesn't believe in happinness as others do not believe in God
(in his time, shortly after French Revolution, the Atheist ideas attracted much more attention
that now, and the idea of "common good", "bonheur general" was commonplace in the
discussions).
Best
Sergei Soloviev