>>6416300From a corporate, business-sense perspective:
Using the original voices costs money, and requires royalties to be paid to the original VAs/studios. Same goes for the music tracks.
Now, Koei did create a lot of original tracks for DW:G2, and Bamco added in some synth tracks that copied the original anime tracks. However, only the original tracks made it in, because Bamco hadn't yet had their corporate structure consolidated properly yet, and licensing didn't carry over to the Stateside house.
Sony happens to have a policy wherein any PS3 and PSP games released for North American consoles have to have an English dub track if there is any voice acting at all. So, that means that if Koei/Bamco were to have kept the Japanese voices in, they would have been forced to pay twice for the voice acting, and this - at the time - was not a wise business move.
Personally, I like the English and Japanese voice tracks about as well, for different reasons. (e.g.: Don't even try to tell me that Master Asia's DW:G2 voice wasn't fuckawesome.) I would relish the chance to buy the JPN dub track via DLC, and possibly any music tracks that didn't make it over as well, if they're not able to put both in the game.