I have never heard of a crash, much less a death, from cracks that started at those slits. Even if the crack progessed all the way around, there's still a steel bolt holding the top and bottom halves together.
I think it's a tempest in a teapot.
You want death stems?
Sorry about the focus on the last one; it's a Rivendell-Nitto lugged steel, handlebar clamp end just fell off.
Ah, this pic shows it better:
Stop worrying about the expander slits and start worrying about
every single other place on a stem!
.