They don't want to "cannibalize" their sales. But so what? Is it that much of a pain to wait one month for a game? If it was like 6+ months, then it would be understandable.
Persona 3 US: August 14th 2007
Persona 3 EU: February 29th 2008
Persona 3 FES US: April 22nd 2008
Persona 3 FES EU: October 17th 2008
Persona 3 Portable US: July 2010
Persona 3 Portable EU: April 28th 2011
Persona 4 US: December 9th 2008
Persona 4 EU: March 13th 2009
Persona 4 Golden US: October 23rd 2012
Persona 4 Golden EU:

?
Persona 4 Arena US: August 7th 2012
Persona 4 Arena EU:

? "2012"

?
Catherine US: July 26th 2011
Catherine EU: February 10th 2012
Devil Survivor Overclocked US: 23rd August 2011
Devil Survivor Overclocked EU:

? "2012"

?
Devil Survivor 2 US: February 28th 2012
Devil Survivor 2 EU:

? "2012"

?
Rune Factory: A Fantasy Harvest Moon =
JPN = August 24, 2006
NA = August 14, 2007
EUR = February 13, 2009
Rune Factory 2: A Fantasy Harvest Moon =
JPN = January 3, 2008
NA = November 18, 2008
EUR = October 8, 2010
Harvest Moon: The Tale of Two Towns =
JPN = July 8, 2010
NA = September 20, 2011
EU = June 29, 2011
Most Atlus games take a very long time and thats why people import the game. Europe has to wait at least 3 weeks and yeah its not the end of the world but if they continue region locking their games then it wont be fun