The finish on the XD is somewhat of a mystery to those who seek to know what it is.
All I can say is that I have owned my XD40 for over three years, and I have fired thousands of rounds through it. I have worn it in the rain on the range, in the summer humidity of south Georgia (damn hot and muggy), did not clean it until over 3,000 rounds to see how it would hold up (and it held up fine, I simply forgot that I was going to leave it dirty, and cleaned it up..duh). I have wear marks on the top of the chamber from it meeting the underneath of the slide during operation, but I do keep it lightly oiled and have NEVER found any rust on it.
I am likening it's finish to the finish on the SIGS and GLOCKS..tough, but not invincible. I don't think any finish is "perfect". Standard preventive maintenance should always be in place with anything metal.