Management has a vested interest in pushing the meme that there are no 10xers: it gives them an excuse for not paying these engineers what they're actually worth. The rest of us just go along with it because it assuages the inadequacy we naturally feel when we compare ourselves with someone like Linus Torvalds or John Carmack.
Clearly there are 10xers, and some of them even post here: Walter Bright, Bryan Cantrill, and Ted Unangst.
Edit:
I'm also not surprised Seibel would say something like this given his past demonstration of lacking social awareness by titling his book of programmer interviews "Coders at Work"--a title that one of his interviewees, L. Peter Deutsch, rightly objected to, much to Seibel's shock. Deutsch in 1984 co-authored the seminal paper on building efficient virtual machines for dynamic languages through just-in-time compilation and inline caching, techniques which ultimately gave rise to the JVM. He deserves an immense amount of respect for this and other accomplishments, and we do him and our profession a great disservice by publicly referring to him as a "coder" or anything else that elicits something less than awe from the general public.
Could you imagine doctors referring to some highly-regarded brain surgeon as a "cutter" or "butcher?" No, instead they talk them up as "brilliant" or even god-like, yet we do the equivalent with "coder" (and allow the media to do it too) all the time.