I certainly can see the value of retention straps for OWB holsters in open carry, including and especially for LEOs.
I was watching an episode of "Cops" recently, where an officer took a guy down and saw a revolver next to him as he was fighting. The officer though that the guy had pulled a gun...officer was surprised when it turned out to be his own service revolver (wow! Cop still carrying a revolver!), which had no retention strap. So, no argument here.