Final Fantasy XI
US Release date: 28th October 2003
EU Release date: 17th September 2004

Super Smash Brothers Brawl
US Release date: 9th March 2008
EU Release Date: 27th June.2008 (Confirmed)

Two major examples of delays on games for a unknown reason. The former, in the year that it took for Square-Enix to press the European Client discs, Final Fantasy 11 fell into disarray, and European gamers paid dearly for this.

Super Smash Brothers Brawl, which has a online tournament option, got a typical 3-4 month delay on the European release.
Now, 3-4 months might not look like much, but various games have at least that delay, with only some games companies releasing the game in the same month.
All the games with this delay have one thing in common... A major component is online play.

Let's say Diamond and Pearl came out in all areas at the same time, and Legendaries were released at the same time everywhere...
Suddenly, You don't have Europe's gamers clamoring for a good deal on GTS and only the japanese gamers actually getting one.

I have made a new rule about how to deal with games...

America, When the game comes to Europe, Be sure to do something for me, and everyone else in Europe...
Be sure to beat us senseless so we don't soil the games that Japan made for you... Apparently, We're all second-rate to you.