Yeah that’s the way it’s designed in Genesis by default. I’m sure there is a way to get the featured image to show up on Posts, but I can’t find the code at the moment.
One way to get around it is to add the same image inside of your Content area…..but depending how you have your blog setup, it could show double images if you don’t have a content limit set.
If I come across the code needed to add the featured image to the posts I’ll let you know.