It serves as a continuation of the plot threads introduced in the previous Checkmate series, which Eric Trautman co-plotted. They're using the JSA since Checkmate is more or less defunct after Final Crisis and main characters like Mr. Terrific are in the JSA anyway. It's Checkmate Lite, if you will.
I also get the feeling DC is experimenting with expanding the JSA franchise, so a mini with a setting that is familiar to a group of fans seems like a good place to start.