It's certainly self promotion, and fairly blatant I suppose, but what about it strikes you as tasteless?
I think his central point - writing more helps you write better; StackOverflow is an easy and welcoming place to write more - is largely true, and I don't think he should be unable to say it just because it happens to promote his own interests.
His writing about truisms and plugging StackOverflow started to become too frequent for me. I can't help feeling that such posts are only written for their advertisement value. I expect some sincerity from blog posts.
Yeah, I agree that the overall utility and technical meat of his posts has dropped off in the last couple of years. (Critics will likely jump in with "What technical meat?") I don't think that's an issue with this particular post, however.
I'm not sure why you doubt his sincerity. Stack Overflow is where he's spending most of his time these days, isn't it? Why wouldn't he be mentioning it in most of his posts? It seemed appropriate for this post. What would constitute a sincere blog post?
Well, the informative thing for me was that one of his original goals in starting StackOverflow was to improve the writing skills of programmers and not just(like everyone would assume) to create a programmer question/answer forum.
I think his central point - writing more helps you write better; StackOverflow is an easy and welcoming place to write more - is largely true, and I don't think he should be unable to say it just because it happens to promote his own interests.