There are members here who run DCC (and sound) equipped locos on DC. Just because you don't do it, doesn't mean that others don't. And as mentioned, that feature is easily disable, so it shouldn't cause you any pain.
I'll give you the decoder test option .. its nice - but I prefer to drop the loco on the programming track and build current file in JMRI
If you are buying a used DCC loco at a train show, a 9V battery in your pocket comes in really handy. DC test (again using a 9V battery) is also very handy quick-n-dirty initial test of a misbehaving DCC loco. I have mentioned that 9V battery test here more than once usually I get a "thank you for the idea".