Honestly it doesn't surprise me that much. The PS2 version was only sold in a big special edition box, which made it $10 more then the Wii version. The most important extra it had was that it included two copy's of the game, one with the English dub and one with the Japanese dub with English subtitles (it was a DVD9 to begin with, so they didn't have room to just put both tracks on one disk). The Wii version was just strait up English with no nice box and no poor mans art book (I also heard that the Wii port isn't exactly perfect).
The type of people that would want to buy Sakura Wars are the type that have been waiting for it to come out since the Saturn, love Japanese dubs and love big box's to put on their shelf
...or your like me and didn't know about the franchise until this game came out in English, bought it on the PS2 only to play it with the English dub, and bought the game purely because it was a new PS2 game in 2010. Which is arguably the last game worth talking about on the system.