On the hard drive side, I do know that the d2 models have fans for cooling whereas the Porsche models are fanless. So the Porsche hard drives do get hotter (although they're well designed to dissipate most of the heat) and require very good external cooling and ventilation (otherwise their life would be reduced because of the heat). The presence of fans does mean some amount of noise from the fans. I personally prefer having fans in an external drive and a possibly longer lifetime and don't bother about the minor noise from them.
It may be something similar with the DVD burners too. Note that optical drives can also get very hot during operation. Apart from this, the d2 models look like they're well above the Porsche models in terms of quality/features - that's why they cost more.