You might not agree with it, but it's most definitely not "arbitrary".
The problem with this thinking is that it relates back to an older system and style. Why can't I access my digitial download of Crysis 2 until two later than the Americans? In the mean time, I could pirate the game, finish it, and decide weather or not it's even worth the trouble and cost.
These small delays are bareable - I can suffer two additional days.
However, there are some simply baffling examples. Take, for example, Pilot Wings Resort on the 3DS. It wasn't finished for the Japan launch date in February, however it will be available for the American release date on the 26th of March. No problem at all so far. The same game - in english - isn't available for the Australian release on the 31st of March, and it currently doesn't have a release date at all. Thanks to regional restrictions, I can't import this title. I can, however, pirate it and use third party firm ware to play it exactly as intended.
Just because it worked one way for so long, doesn't mean that the situation doesn't need to change.