I think it's mostly a "why are you telling us? The author of the article might not ever even visit HN. Email them." reaction.

FWIW, the author is on Hacker News at https://news.ycombinator.com/user?id=luu.

Moreover, it is non-obvious how to contact the author via private email. The "about" section of the blog just links to a twitter account:

http://danluu.com/about/

This is especially strange as the author then mentions email there, without providing an actual email address:

| Please ping me on twitter if it looks like your email got eaten by my spam filter

Maybe the author expects a reader to brute-force lots of addresses "something [at] danluu.com"?

I'd prefer if he just give his address, but in Dan's defence he does offer some pretty clear hints in his profile page: "Email is my full name @ gmail." https://news.ycombinator.com/user?id=luu

His email address is also given prominently on his linked resume: https://github.com/danluu/tex-resume (periods are optional in Gmail addresses)