Very interesting ppppilot, thank you!...didn't know. So then - the CRJ design or subsequent certification requirements required that the potential for deployment be addressed, possibly due to control issues, (speculating) whereas the MD series did not... For the Airbus 320 series, weight and software design were likely easily-resolved issues. For the Embraer 175/190 series, FADEC commands IDLE thrust if an inadvertent reverser deployment is sensed.