It also suggests landing Conf before gear down.
You can't extend either flaps or slats with the loss of DC ESS and DC2, hence the "must".
I've looked at our FCOM and for the most antiquated aircraft in the fleet (MSN ~1000), this warning still applies. For all the others, it's been deleted.
To be honest, I don't think you can really get into the DC EMER CONFIG by itself. The "loss of DC ESS" at gear down is just as likely to be "loss of AC and DC ESS", meaning you're landing the aircraft on computers supplied by the HOT buses and standby instruments. All radios (nav and comm) are lost. But you get to keep the clock. ;-)