With all due respect, just because you don't know that 'Jap' is considered highly offensive and derogatory doesn't make any difference, it's just your lack of knowledge. The term is considered highly offensive by Americans of Japanese origin. As far as fewer keystrokes, so is 'Paki' for people of Pakistani origin in the UK and that's likewise considered offensive by them. All four terms, with the other two you mentioned, were or are used by members outside an immigrant group to make sure the members of the immigrant group understood/understand they aren't fully accepted as 'part of the club' in that country, and people always take offense when it's implied they don't belong where they live or even where they grew up.Of course not. I will try to remember.
But let me also say that the term Jap is not generally accepted as offensive or derogatory. It seems to me the term was commonly used until WW2 when it became politically incorrect. This is quite different from Kraut or Wop as these were meant to be offensive from the start.
For me it is just a few less keys to tap.
'Politically Correct' IMO is a way overused term, and is often used to imply that 'somebody else' is being 'too sensitive' about a particular term, when in fact the speaker would be highly sensitive about other terms, opinions, etc., almost everybody is, about something. Or to put it another way, some guy in a trailer park somewhere thinks it's 'PC' not to use n***er to refer to people of sub-saharan African origin. Calling something PC is, by itself, essentially meaningless IMO.
Joe