Personally, most gifts I've given or received have been items which I didn't need and not at any great cost. I still gave them to a person of my choosing. So when dead and in need of nothing, one's wishes to give to a particular person, charity, or even hypothetically anyone should be respected.
If John owns an item, he can say what happens it. So if he says to an notarised person 'when I die X becomes property of my son James' then that's simply respecting his wishes over his property.
Is it much different if John choose to give something away moments from death, or if he asks someone else to arrange the giving on his behalf after death?
We respect the wishes of the dead because it's part of the continuance of life and civilisation (which is itself fundamentally the store and passing down of value, I.e. inheritance). The same reason we'd honour someone who died for freedom, or honour the funeral wishes of a family member. Their wishes are worth much to everyone who knew them. The same should apply to personal property.
I think I'm stabbing in the right direction. A better answer might come from a better read or more philosophical mind than mine.