Maybe he just figured "children" in their 60s should be on their own by now, anyway.
When my mother died, she left more $ to my alcoholic (then 62 y/o) brother who is unwilling to support himself than she did to my sister and me. It was a little annoying, but we understood that it was her money to do with as she wished and we had no right to it anyway. Not surprisingly, though, he's spending his inheritance at a local bar. 
Actually, I can understand the thought process here....regarding the parents attempting to 'protect' the brother.
One of the most upsetting things is to see the 'Finish Line' ahead and look to the sidelines and see one of your children appear to not be able to take care of oneself.
Feeling guilty, when physical/learning disabilities are present, you hope and pray the other siblings will make sure they don't end up "on the street".