USB - S is for "serial".
It's already like that,otherwise you could connect only one device per header. Forget any kind of hub.
yes, Serial and not parallel and when you're using a splitter cable you're using it in parallel...
Why do we stupid people than use always electronical USB hubs instead simple splitter cables?
When you have two headers are these headers always two from each other independent electronical USB channels.
Ok, it seems I'm wrong because you're saying it is always working. Please light my fire and describe the technical theory why it is working. I'm always interested in learning new things.