The frustrating thing about this is SO has the potential to be much more valuable than a blog post. An SO answer will get a lot more eyeballs than a personal blog, and has built-in and well-understood capabilities for community collaboration and updates.
Say you find a bug with Product X v1, create a workaround, and post it to your blog. In V2, the problem has been fixed, or exists in a slightly different incarnation with a slightly different workaround that someone figures out only after reading your content. Maybe they'll leave a comment on your blog about it, but you don't really have any incentive to update it. If your post was an SO question, they could post another answer or make an edit, and the page becomes the canonical source for information about the bug.
I agree with you in theory, but it's also important to understand the SO perspective on this issue. It seems like they believe allowing the community to "drift" by not modding things defined originally as off-topic will be harmful to the community in the long haul.
How many times has HN discussed the digg/reddit/HN decline in quality as the population grows?
In their minds (and I have to give them the benefit of the doubt given their awesome accomplishment!), keeping strictly on topic is one way to prevent the point of the site from drifting.
It may be that the SO people "want" is a better one. But that's the decision that Atwood & co. have made. To wish for a SO that allowed off topic responses is to ask for a different product.
Say you find a bug with Product X v1, create a workaround, and post it to your blog. In V2, the problem has been fixed, or exists in a slightly different incarnation with a slightly different workaround that someone figures out only after reading your content. Maybe they'll leave a comment on your blog about it, but you don't really have any incentive to update it. If your post was an SO question, they could post another answer or make an edit, and the page becomes the canonical source for information about the bug.