Many people in this community think Atwood is a retard because he writes about stuff he's not an expert in, and because he uses Microsoft products. I venture to guess that many people here think he's not of the caliber of programmer that YC invests in. He has clearly proven them wrong.
I think you're knocking down a strawman; many people don't think he's a retard so much as a mediocre author who writes a sometimes exasperatingly mediocre blog.
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.
There's no doubt access to a large audience helped get some publicity and users early on. But to be fair, Stack Overflow worked well and was useful on day one. We've seen startups basically fold on the first day when things don't go smoothly. The site crumbles under load. There's no content on a user-generated-content site. Maybe the thing flat out doesn't work as advertised. Some of them eventually overcome these problems only to be ridiculed for it over the next year. The Stack Overflow launch was handled incredibly well. I would attribute their success to much more than the size of their audience.
That's not being fair, that's being contrary. If StackOverflow was a stupid idea or poorly executed, no one would use it. Yes, they announced it from a pretty tall pulpit, but if no one cared what either of them had to say--for or against--no one would care to read their blogs, either.
Sure, it's being fair. Before we go off and pronounce that "Jeff Atwood has proven everyone wrong," let's keep a few things in mind. Also, having a lot of readership does not prove someone is a top shelf programmer.
To be honest, this is not even something that Joel and, perhaps, Jeff haven't said themselves.