Holding your readership in higher regards than a meaningless metric can be worth a lot in the long run, too.
I actually looked for the twitter button on his site so that I could follow him - since I did enjoy the post and would like to see more from him. Didn't feel manipulated though.
The way he embedded the suggestion seemed contrived and inorganic to me. If some one puts a link to their Twitter account beneath a post, I know what to do if I want to follow them because of their output.
If I have confidence in my output I will trust my audience to find the right degree of involvement they want to have with me. No need to push it. Maybe I'm weird that way, but I think the OP knew exactly what he was doing, and stuff like that rubs me the wrong way because I find it undignified, harshly put.
You don't understand why people promote themselves? You made it to the end of the blog post, which likely indicates that you enjoyed the content. Why wouldn't he say "hey follow me on twitter so that if I write another post that doesn't make it to HN front page, you can hear about it," to try to get some extra followers? Would you prefer he ask you to follow him at the beginning of the post?