According to Gamespot, UFO Interactive, the same company that brought Raiden III to the states on the PS2, will now be bringing Raiden IV for the Xbox 360 to the states on September 8th!
http://www.gamespot.com/xbox360/action/raideniv/index.html
I'm assuming the sales figures for Raiden Fighters Aces must have been good enough to finally convince them?