Spolsky is really more of a silent partner in this (maybe not so silent publicly, but the impression I get from their podcasts is that he is involved only on the business end).
None of that means he can't be a brilliant programmer. I'll admit to being a little surprised that SO took off as it did, and I certainly don't think that being relentlessly hyped again and again by both blogs explains all of that success. But I'm not sure why that proves me wrong; am I supposed to start liking Atwood's blog now? I opened it to have another look; the top post starts with a pronouncement that "abstractions are powerful things" (oh God), and then goes on to tediously argue that they invariably leak, but are still powerful things. No thanks.
To be honest, this is not even something that Joel and, perhaps, Jeff haven't said themselves.