Games are never affected by your console's/handheld's OS. Function of the X/O button is always dictated by the game.
Not completely true (as said above) and sometimes, it even makes things worse...
I mean, on my japanese PSP, to save in an european game, I had to:
- press X inside the game to select "SAVE"
- then press O to validate the save (since it's an OS dialog)
- then press X to quit the OS save dialog
- then press O to quit the Game save dialog
That's just... awful.
I've always hated they switched the buttons when they introduced consoles in western countries. Made no sense at all.
Besides, it seems that games just swap the buttons even if that makes the gameplay less intuitive. In Japan, Minna no golf use O to hit the ball, and Triangle (upper button) to increase the power, and X (lower button) to decrease the power. Logical.
Western versions (Hot shots golf / Everybody's golf) switched the X and the O, and it seems far less logical this way.