I don't think we should get to hung on on is the GTI better than the GTD, is petrol better then Diesel, as these arguments have been done to death over many years. Different people have different expectations, wants and aspirations over their cars. Some prefer petrol, some diesel - who are we to tell them they are wrong !
I think Monkeyhanger hit the nail on the head though. Previous to the MK7, if you wanted the GTi looks (bumpers, side skirts etc) you either had to buy a GTi, or retro fit the parts at quite an expense. VW have now seen fit to produce both GTi and GTD models which are visually identical (bar exhaust pipe arrangement and red stripe on front bumper). Even the 19" alloy wheel options are the same. Now everyone can pick the car of their choice, which is exactly how it should be.