Why do Americans say "burglarised"?
If I was mugged I wouldn't say "oh no I've been muggerised."
If I was killed people wouldn't say "oh no he's been killerised."
If someone was raped people wouldn't say "oh no she's been rapistised."
And also, why do Americans spell it with an S when they change most spellings to a Z?
Just another example of how inconsistent American English is.
I actually assumed it was spelt with a Z, but the Yahoo Answers (An American website) spellchecker said it should be an S.