A comment on the previous post about Hamapil....
The theme of Hamapil is supplication of Hashem that he should guard us in our sleep. This does not seem to be reflected in the psukim we say in Baruch Hashem li'olam. Which re-establishes the question of why some don't say it.
One can add that according to some more kabbalistic sources one shouldn't say it after chatzos [with shem umalchus] so if it is already after chatzos there are two reasons not to say it [i.e. the custom not to say it at all and the custom not to say it after chatzos]. Not that I am anybody but I say it no matter what in keeping with the psak of the shulchan aruch ...... and the gemara