Although I haven't heard anyone talking about having seen or wanting to go see Jake Gillenhal's Prince of Persia, I have overheard people questioning the producers' decision to cast a white guy as the prince of persia, who was presumably a persian....? maybe? But I know why they went white guy, they were just trying to stay true to the franchise.
In creating movie adaptations of books, plays, video games, telenovelas etc. the man in charge of the adaptation has always got to be balancing the conflict of staying true to the original story and staying true to not making a movie that totally sucks.
It's a very difficult line to tip-toe around, even for those with the best tips. A lot of times, in order to not to anger the contingent of pre-existing fans, adaptations follow the established plot too literally (watchmen, passion of the christ) and suffer the chat-room consequences. In other examples, movies such as those of the Bourne trilogy, which I hear hardly resembled themselves in book form, opt out of the old plot, commandeer the name and make something new up as they go.
The men and women in charge of the Prince of Persia had to make one of these types of decisions: "do we cast a bad-ass non-white guy as the lead and make a good movie, or do we try and stay true to the franchise and go with a white guy, which'll make our movie look unavoidably stupid." Because as you can see in the picture above, in all of the Prince of Persia video games the prince is white, look at those white arms..!
So, it seems like the producers chose the consistency of the franchise over the profitability of the franchise. At least they didn't choose toby mcguire though.