Juding from your reply, I guess you have never been in a porsche show room let alone a porsche car. Porsche cars do in deed have an option for DVD and sat nav, no different to other decent make cars, It just depends if you want to pay there prices, and you like the systems they offer.
personaly I prefere the Avic D3, it has better sound qualitys and gives me more options to fit after market accessories to it, like an I phone or blue tooth control. along with an amplifire and sub etc.
The next time you pass a porsche show room pop in and ask how much the sat nav DVD option cost.
Then price