Duo-RX not requiring Arcade card???

Hmm, I did not know you can play arcade card only games without the
card on a Duo-RX. It's a requirement on the Duo-R but I've never opened
my RX machine to test it (cos it's new and I like to have it in that
condition) ;)

I thought the only difference with the Duo-R and RX machines were entirely
cosmetic?

Will/