Plenty of studies have shown that it's true. If you can't see it, maybe you're one of the less productive ones?
I can imagine someone being more productive because he has experience with the business, ie. because he knows a lot he doesn't have to have everything specified or call for meetings. But when it comes down to just coding, I can't imagine someone being 10x more productive than the next guy (unless, as someone else mentioned, the next guy just sucked). Coding isn't that hard. It's a trick you can teach virtually anyone. After years of programming people will develop their own style and some styles better match a certain project than another. But 10 times difference? I'd like to see those studies.
Also "If you can't see it, maybe you're one of the less productive ones" is uncalled for.