I've had no real problems getting a spark from the ferrocerium rod, although now that you mention it, it did take two or three tries. I don't know if it's a "coating" as such, or just oxidation, but you're right, it comes off with a good scrape.

But the "flint striker" on the base of my matchsafe has been scraped till it gleams, I still can't get a spark from it. <img src="images/graemlins/frown.gif" alt="" />