There is no logic behind JAP being a racial slur. It is a shortened form of JAPan(ese).
Calling JAP a racial slur is like calling GER a racial slur. It doesn't make sense.
"Racial" slurs, such as 'redneck' for someone from the south of USA, have some logical origin, something about being in the sun for too long and their neck becoming sunburnt.
Some people may take offense to the word JAP, and I can't stop them from doing so. But some people may also take offence to the word Tablecloth, and there isn't anything I can do about that either.
As an Australian, I have certainly heard JAP and NIP used derogatively. This does indeed stem from world war 2, and the fear of Japan so close to our borders, as much as anything the Japanese actually did or didn't do.
But I have also heard 'coon', a brand of cheese, used derogatively. IT should be no surprise that the company has not sought to rename its brand.
http://en.wikipedia.org/wiki/Coon
tl;dr, get over it