George - nothing to do with men vs women; in Europe the sizes are unchanged, so I know I'm still a French size 36 (German 34, Italian 38) which is what I was in high school. These sizes used to be indistinguishable from an American 6 (French size minus the 30, don't ask me why) until about a decade ago, when I discovered I'm - suddenly! - an American size zero.
Fortunately I've not turned into the invisible man, since the French still manage to get my size at the correct 36, and I simply agree with the other folks here who said the re-sizing is a pure marketing ploy.
Does it work, though? How can women shorter than me (I'm 5 ft 10) weighing a lot less than my 110 lbs, find clothes sized under "zero"? Are there any negative sizes? This whole thing is a transparent scam and I hope somebody fixes it soon.