I just checked one of my Android apps and it says the same thing as your does, 0 excluded. I believe that when users go to Google Play, devices that don’t support your apps features will not have an install button. This appears to be a way that you can manually exclude devices. Later if you find that the ObbieWoobieCheap Tablet is crashing a lot, but it’s still an ARMv7 device with an underpowered GPU, then you can add exceptions yourself as you need to. In other words, you generally don’t need to worry about this.
Rob