yes, i've seen a few examples of this kind of thing. in fact, i'm married to the son of the 'wicked stepmother' - the second wife, who will inherit everything from dh's stepdad, leaving HIS daughter with nothing.
fortunately, we are talking pennies, not even pounds, but anything left from the first wife (even any trinkets) has either gone to dh's mum or been thrown out. dh's stepsister was also thrown out when 18, and 'never existed', even though as a teenager she was made to take care of dh (several years younger) AND the house!
in spite of the fact that she 'never existed', WE get on really well with her, spent last Christmas with her, and she has no financial needs. however, her dad is elderly & v frail, when he dies, it IS going to be difficult - dh's mum will inherit everything, and won't even acknowledge that her step daughter exists, so won't let her go to the funeral.
the lesson is, IF you have specific wishes about what will happen to your money after you die, you need to write it down v clearly in a will. You can't take it with you, and once you die, you don't get any say in what happens to it either.