It's all in the design. Look at it this way:
Compare a Huyundai Sonata (or whatever their best sedan is) to a base model BMW like a 318. If you run down the options list and compare features the two cars will look the same-leather seats, CD changer, climate control, similar size engines, sunroof, etc. But if you drive both cars to side by side you will find that something didn't make it on to that spec sheet
. The BMW clearly drives differently and has a better quality feel.
Same is true of the Duratrax vs. Losi XXX. It should also be noted that the Duratrax is a very close copy of a Losi XX, the XXX's predecesor.