No, it's not a typo - I got it from the horse's mouth (David Laurent) - but it's nothing to be alarmed about
In DCC, power / message is a +/- 18 V (or so) square wave : it just depends on the internal circuitry of the base unit whether you obtain it from two opposite polarity PSs or a single, double ampacity PS
So, this really means that 15 cars, with NC1 / NC2 motors, are happy with 10 A - what's important is that PSs should be stabilized (not wall warts)